Sorry i have not much knowledge about it but i think Windows server 2008 r2 is a server and windows 7 is not so i think they are different.
Windows 7 SP1 is the upgrade version and more or less the downloading procedures are almost same but you can find some extended features in the upgrade version...
Windows Server is, obviously, designed for servers and has "normal" features disabled by default I think (eg Aero)
Windows 7 is a desktop OS where as 2008 R2 is a server edition. Windows 2008 R2 basically used for purposes like web server, production server etc. There is a big difference between SP of Windows 7 and that of 2008 R2 2008 R2 is the latest release of Windows server edition.