The argument raised by Tai-Hao against using the Windows logo on their new keycap sets was that it's trademarked, which is why they shipped blanks (where in the past, they produced keycap sets for Focus with proper Windows logo keys included, but pad printed). It's a strange one, as you'd think that Microsoft would be keen to have their logo on every keyboard, but then they apparently introduced a stupid rule that the Windows key had to have a physical Vista bubble on it, and that bubble annoys some people more than the logo itself (personally I couldn't care less). Tai-Hao have found some compromise with recent keycaps but it's still not the full Windows logo.
If I'm going to have the Windows logo, I'd rather it be the most recent one.