IMHO, moving is not required (at least for now). Although VS2010 is the latest one, there many people using VS2008. As you know there is no backward compatibility for VS series, which will bring some problems to that individuals driving VS2008.
And one more thing is .NET versions mess. Moving to the new version will force existing products to be recompiled (an easy way that I think will be hardly ever achieved) or even totally rewritten.
Surely, such move must be done, but with care. Best way here is to provide as many versions as possible and analyze the downloads for each. Such approach will show you whether you need to move or not.
Also want to add that this is my opinion that may vary from others'.