No time to learn every version
My shop operates on low margins, and we support many Microsoft apps. We just don't have the financial or physical resources to keep up. We just got most things converted to .NET 2.0, but we don't have time to actually reengineer the code to use the new features. Now 3.0 is old and 3.5 is coming. They don't even have classes in 2.0 anymore (like what the differences are between that and 1.0). By the time we get to 3.5, they'll be on version 8. The new tools are great...I can't wait to use them someday.
The pace is blinding, but it doesn't look like Microsoft will slow it down anytime soon.