Some time ago I've run into this interesting presentation from Microsoft Tech-Ed Israel, called The amazing world of …Microsoft Secure Remote Access & Application Security with IAG & UAG.
It contains some nice info about the two products, about Microsoft Secure Access Strategy. There is also a "UAG" vs. IAG 2007 table.
You can download it at:
http://download.microsoft.com/download/a/7/c/a7ccc02e-9404-4008-ac61-2bcd696c92ec/SEC479.ppt