Nope. You can install Windows 7 upgrade with a clean install no problem. I just did it, as you can't upgrade from 32-bit XP to 64-bit 7, and that's what I wanted to do, dammit! <laugh>
Follow this tutorial:
Clean Install with a Upgrade Windows 7 Version - Windows 7 Forums
I did, and it worked like a charm, though I did in fact have to use the registry workaround (see option 3). Also, make VERY SURE you pay attention to the "do not check the automatically activate windows when I'm online" part when you install.
GL!