Enterprise apps using IE have 1/100 of the design complexity of sites that are affected by these changes.
I just ran CLOC. We have 6.2 million lines of code in 14 different languages!
And yes, things break all the time, often for unknown or unexpected reasons, and it's sometimes close to impossible to figure out why and fix the bug.
The enterprise software world is scary.
Oh, and the entire site didn't work in IE6, it was developed / tested entirely targeting Firefox, despite the IE6 requirement being in the spec (and it ONLY needing to work with IE6).
the Outlook web interface was miles ahead of anything in the consumer space for years.