Well, actually MS is gonna emphasize on Windows Starter (netbook) Home Premium (all home-oriented computer) and professional for people who need domain networking.
Professional: All the features of Home Premium+Some Business connectivity stuff (domain,etc.). They are not going to promote Ultimate like they did on vista..
READ HERE for more info: http://www.winsupersite.com/win7/win7_skus.asp
Like he said every version is a 'super-set' of another... I think this brings back XP days: Home Edition: Home people; Professional: For Organisation but got everything home edition has. Only thing is Starter is out of the picture... I HOPE OEM WILL NOT SUPPORT STARTER! (MS should at least put 'aero peek' in it.. 7 looks ugly wihtout 'peek' with icons only at the taskbar).