It's a subtle change but an important one: Apple's published Windows system requirements for iCloud are a bit different than they are for MobileMe and the current version of iTunes. Per the company's press release:
Using iCloud with a PC requires Windows Vista or Windows 7; Outlook 2010 or 2007 is recommended for accessing contacts and calendars.
Emphasis mine. What's missing? Only the world's most popular operating system (still!), Windows XP. While iTunes 10.3 and MobileMe both include XP SP 2 in the
