First of all, since the actual total sales of DSLRs world wide isn't available we have to figure out a way to get a close estimate. My approach at doing this is to use sales results that Amazon reports. I chose Amazon because it is the biggest online retailer world wide ($34.2 Billion USD in sales in 2010 and grew by 34.5%) and they are 3.4 times bigger than the closest competitor. So I claim that Amazon results are a very strong indicator of what's going on in total world wide sales.
The other claim I make is that the collective wisdom of all camera buyers has the effect of choosing the DSLR with the most value for the money. That is, hundreds of thousands of people are studying the specs, considering the prices and voting with their money. Note this is NOT the best DSLRs, just the best value for the money.
Here are the top 5 DSLR bodies as indicated by Amazon sales: