what's the difference between Windows 7 retailer disk and MSDN windows 7.ISO image file

1. as Microsoft company assigned timetable, the newest os windows 7 will be released on 22nd october 2009 worldwide. Out of curiosity, i borrowed an original windows 7 disk from my friend which he bought a couple of months ago, then i used the program to compare it with MSDN windows 7 ISO image file. To my surprise, everything is the same except the windows 7 retailer disk has "Windows Anytime Upgrade on the cover", which means you can pay to upgrade to any higher version online and it has got a Microsoft genius key in it .So as matter of fact, the windows 7 retailer disk and "MSDN" windows 7 ISO. image file are exactly the same.