Hormone D is made from vitamin D
Vitamin D and hormone D are metabolically linked by one enzyme. Testing only the vitamin does not prove a deficiency of the hormone. There would be more children with rickets if the food supply or sunlight supply was inadequate in vitamin D or cholesterol. Statin drugs stop the liver from producing cholesterol so people taking statin drugs long term could be more at risk for low levels of both vitamin and hormone D. However they would also need to be avoiding sunlight, dairy products, egg yolks, some types of fish and other vitamin D fortified foods like breads and cereals. If an epidemic of rickets isn't a problem  then probably a reasonable amount of vitamin D has been available over the years. There is certainly an association between chronic disease and low vitamin D levels but it has not been adequately proven that low vitamin D is causing the chronic disease or whether it is a side effect of some other condition. It has been proven that the enzyme that converts vitamin D to the active hormone D is made in some types of cancer and autoimmune disease. There are two tests necessary to prove a deficiency of both the vitamin and the actual hormone D. It has been proven that excess hormone D can cause chronic degeneration from excess calcium leaving the bone tissue and it causes pain. Two tests are needed to show whether there is deficiency of vitamin D or whether there is actually excess hormone D. The test for vitamin D levels doesn't measure the amount that was converted into hormone D which is the form that signals bones to release magnesium and calcium from long term storage. It also signals the intestines to preferentially absorb more calcium than magnesium. Magnesium is inexpensive but it isn't absorbed well when there is also a lot of calcium in the food or supplement or when there is excessive hormone D levels. Two tests for D can show who needs further testing vs who needs supplements or diet guidance.The good news suggested to me, by the limited number of cases of rickets in comparison to the large number of people with low vitamin D levels, is that having both the hormone and vitamin levels tested would show who needs a vitamin and who might benefit from more testing for underlying issues.
Testing for chronic infection or cancer can catch treatable problems in much earlier stages of disease before osteoporosis or soft tissue calcification are allowed to happen. If the hormone level is elevated and the vitamin is low there can be a treatable reason why the enzyme between the two forms is overactive. Or sometimes there is an issue with too little activity by the enzyme that breaks down the hormone and too little enzyme activity allows the hormone to build up to excess levels.
Making too much active hormone D or not breaking down the excess can lead to worsening chronic disease over time. Measuring both the vitamin and hormone levels of D can show who needs a vitamin and who might need antibiotics or other treatment and who might be harmed by the use of excess supplements of D over time. So, yes, vitamin D is important and many people have been found to have low levels but we haven't been measuring the level of the active hormone in many research studies and it is more powerfully active within health and illness.
Agribusiness and processed food are an essential part of the food supply. Improving food labeling would help people with food sensitivities or allergies to avoid risk without requiring all processed foods to change ingredients. Standardizing fortification levels helps with menu planning for a healthy diet for individuals and residential facilities.
Corporate profit and national viability is affected by the cost of health care and that won't get cheaper if the same wrong solutions are pursued. One vitamin or medicine can never grow a body or give the body the nutrient building blocks that are needed for healing.
Multiple nutrients are necessary for preventing chronic disease and repairing health. Recognizing that there is a link between elevated hormone D and low vitamin D will be important for the long term effectiveness of any health care system for any business or country. Pursuing vitamin D supplements as an easy solution to chronic disease has not been working and any one nutrient solution will not work to build health. Magnesium or iodine are not single answer solutions either. Vitamin K, selenium, zinc, vitamin C and B's and the essential fats and phospholipids are necessary as well as adequate calories and protein. Many nutrients working together help maintain quality of life and reduce pain and chronic degeneration. Basing health care on medical and surgical solutions alone can not solve or prevent all types of health issues. Those types of solutions are needed for acute repair but chronic degeneration needs prevention strategies and many nutrients working together within the body.
/Disclaimer: Information presented on this site is not intended as a substitute for medical care and should not be considered as a substitute for medical advice, diagnosis or treatment by your physician./
Canadian Medical Association Journal (2012, November 5). Low vitamin D levels linked to longevity, surprising study shows. ScienceDaily. Retrieved November 11, 2012, from [sciencedaily.com] *The study control group had higher levels of vitamin D and had more chronic concerns. Low vitamin D levels is only important if there is also low hormone D levels.
van Heemst D., Leiden Longevity Study, Longevity Research Background, in Dutch, [langleven.net]
Lazol JP, Cakan N, Kamat D. 10-year case review of nutritional rickets in Children's Hospital of Michigan. Clin Pediatr (Phila). 2008 May;47(4):379-84. Epub 2008 Jan 11. [ncbi.nlm.nih.gov] *The charts of 58 children with rickets diagnoses were found for a ten year time period at one hospital, 96% of them were exclusively breast fed and ethnicity suggests many may have hard dark skin tones which blocks sunlight production of vitamin D. Ideally vitamin D supplements would be recommended for exclusively breast fed infants during preventative nutritional counseling. So roughly 6 children per year at a large hospital with rickets - that is a much smaller number than "35% of American Children." 
Bener A., et al.,Vitamin D Deficiency as a Strong Predictor of Asthma in Children. Int Arch Allergy Immunol 2012;157:168–175 [content.karger.com] *The study participants were found to have lower vitamin D levels than the control group but they also were found to have lower magnesium levels and increased bone turnover levels which would suggest to me they actually had elevated hormone D but that wasn't tested. Magnesium is cheap but it isn't well absorbed if there is elevated hormone D due to some other unidentified issue. Vitamin D supplements and food were used by a significant number of the study participants. Excerpt from this paper that is in reference to a different paper: "Litonjua and Weiss  found that 35% of American children were vitamin D deficient and these children were at a greater risk of severe asthma attacks."
Hashimoto Y, Nishimura Y, Maeda H, Yokoyama M. Assessment of magnesium status in patients with bronchial asthma. J Asthma. 2000 Sep;37(6):489-96. [ncbi.nlm.nih.gov] *The magnesium levels were similar between asthmatic and control groups in the serum blood test but the magnesium level inside of red blood cells was lower in the asthmatic group.