SQL Server 2008 R2 has just released to manufacturing (RTM’d) as I write this. With each new release, we make changes to the “Editions” we offer.
A SQL Server “version” deals with the major changes in the product – and “edition” is a set of features and capabilities within that version (you’re welcome).
So… definitely run over to http://msdn.microsoft.com/en-us/library/cc645993(v=SQL.105).aspx and check out the changes. For instance, did you know that SQL Server Express now supports 10GB databases? Well, then get over there and read what each edition does.