Yes it is. It works too. I upgraded just so I could run the SDK. 40 bucks is not too much to ask for a sdk that comes with windows 8.
To me it is not about the money. It's about forcing me to upgrade my system when I'd rather not do an upgrade right now. I have a lot of applications installed and it would take a lot of time to upgrade, especially since I prefer to do a clean install. I have a ton of music applications with dozens of paid for plugins that each have their own installer with different activation schemes. Every time I need to go through this it is a major PITA.
I realize no-one is forcing me to use the WP8 SDK, however the fact that there is really no technical reason why Windows 8 should be required other than for emulator support really ticks me off. Not everyone is ready for a major OS upgrade.