In a post on the Windows Blog, Microsoft announced that Windows 8 would be called Windows 8, and that there would be only two generally available versions for retail customers. It also used its Microsoft Management Summit keynote to name Windows Server "8" as Windows Server 2012 (to align its name with both System Center 2012 and SQL Server 2012).
The two retail versions of Windows 8 will be called Windows 8 and Windows 8 Pro. Windows 8 is analogous to the current Windows 7 Home Premium, and Pro to Windows 7 Ultimate. Most home users will use Windows 8, with Pro adding Bitlocker and domain access. Media Center has been removed from both versions, and will only be available as part of a downloadable Media Pack for the Pro edition (which is likely to be an additional cost). Microsoft will be shipping two additional versions, Windows 8 RT for ARM devices, which will only be available to OEMs, and Windows 8 Enterprise, which adds desktop management tools for System Assurance enterprise licensees.
In practice there's not a huge change from the way Windows 8 is being sold, from the ways you could buy Windows 7. There were only three retail SKUs, Home, Home Premium and Professional (Ultimate was a limited edition that was really a consumer version of the Enterprise SA-only release). Starter was OEM only for Netbooks. What's happening with Windows 8 is pretty much the end of the Home version – which very few people bought – with Enterprise features arriving in the Pro version.
Microsoft has produced a handy table of the capabilities of the various Windows 8 versions:
It's interesting to note some of the capabilities of Windows RT – especially the device encryption options – which appear to be much more closely aligned to a smartphone-like management scenario, based around Exchange ActiveSync.
Incidentally, there's been no official announcement of the difference between the device encryption in Windows RT and BitLocker in Windows 8 and Pro but we do know a few details. Both ARM and low-power System on Chip 86 tablets use firmware TPMs for encryption (ARM uses the TrustZone for this). BitLocker is managed by Group Policy. Device Encryption is not managed by Group Policy (nothing on Windows RT is); if it is managed, it will be by EAS, but it's likely that Device Encryption will be turned on in Windows RT without the option for users to turn it off.