Sardi's premise seems to be that "cancer experts" are downplaying vitamin D's effectiveness as a cancer preventative out of selfish motives. This explanation will play well with the Conspiracy crowd, but not with anyone who looks at the evidence.
The latest study (which finds that vitamin D supplementation may be useful in preventing colon cancer, but doesn't have an effect on overall cancer mortality, looked at _many_ more cancer patients than the initial study that Sardi is ballyhooing. It isn't the last word on the subject either, but the evidence to date doesn't suggest that we should necessarily start taking tons of vitamin D. It was once thought that vitamin E was a "magic bullet" against heart disease - until more evidence accumulated and high-dose vitamin E was actually found to not be of significant benefit, as well as causing worse health in some people.
More on the vitamin D studies here, for those interested in Science and good health, rather than Mike Adams Bizarro-Conspiracy World: