http://store.microsoft.com/microsoft/Windows-7-Professional/product/B985134B Microsoft's pages now specifically say 32 and 64 bit are included on one disc. Perhaps Amazon will eventually specify this also.
Each version of Windows 7 comes with BOTH the 32 and 64-bit discs. They're on seperate discs but your product key is interchangable (you cannot instal 1 machine with 32-bit and 1 with 64-bit however). I just got my copy of 7 Professional through the MSDNAA and I have to tell you: BEST OS from Microsoft yet!
Wow, that's surprising! I thought Microsoft would milk it as far as they could go by splitting up the 32-bit and 64-bit versions of Windows 7 and offer at least 6 different versions of each bit version! (Ex.: Cardboard Basic to Mega Ultimate in x32 and x64 for a total of 12 versions or something?)