I am trying to figure this out as well. I can understand there are problems - layout issues, popup windows blocked, activex controls denied permissions. Howev

I am trying to figure this out as well. I can understand there are problems - layout issues, popup windows blocked, activex controls denied permissions. However all these seem like things that are either totally cosmetic or could be fixed with relatively minor hacks - most of them with just registry configurations or an alternative stylesheet here and there. If people could name actual technical reasons why apps break then I'm sure a group of interested parties could quickly form an open source project to develop a compatilibity layer / plugin / something that would bridge the IE7 - IE6 gap. But nobody ever seems to get down to that level of specificity. I have to think that it's really mostly about corporate inertia and lack of desire rather than actual real technical challenges.