The Vista strategy is very simple, attempt to make a second sell of their product after you have purchased it from the reseller. Most computers are sold with Home Prem or Business but few have Ultimate. Microsoft expects the user to want to upgrade their home prem when they figure out that they want to take it to work (or more likely a school environment) where they need the domain features to connect. A lot of campuses require Windows Pro for domain access and stuff.
Microsoft wants to itemize the OS where you pay for each of the features you want. Supposedly Windows 7 will be available in a basic install then each component you want will have to be purchased and installed separately but that is rumor.
The business version still has most of the multimedia WMPlayer just not able to decode DVD movies. Of course most computers sold with DVD drives on the computer have a separate DVD player installed. You really could not tell the difference between home and premium until you attempted to start the media center app. I always tell people to just purchase the Business Vista. If you want a media center experience install Beyond TV, Sage TV, etc.
A more sinister feature of Vista is the capitulation of the OS to media content providers. Apparently media center enables the dreaded broadcast flag and other right restrictions to record TV. Also music and other video files will fall victim to these restrictions to prevent "Sharing" to your friends and via peer to peer networking.
I could go on and on...
