The 64-bit version of iTunes is a mixture of 64-bit and 32-bit componentry. You'll also notice on your PC that some of the componentry for iTunes itself is installing in the iTunes folder in the Program files directory (such as the miniplayer). The GEAR drivers used for burning and importing are 64-bit. The iPod service is 64-bit. AMDS is 64-bit. Bonjour is partially 64-bit.
It's normal to see the itunes.exe process running as 32-bit on a 64-bit system.