For a product like IE, it makes a lot of sense to have long release cycles.  Look, I know the armchair dev crowd (like me) likes to see fast releases and a lot of new stuff.  But the BigCo's and the financial people and others rely on the browser to keep their business running and want to have their browser continually patched and secure.  Microsoft isn't going to keep too many browsers around and supported, so it is sensible to keep releases on a slow and steady pace.

From the MIX talks, it seems like Chris Wilson's team is going to work on Standards compliance and try to figure out a way to allow conditional comments or something of that sort put the browser into a new mode which is more compliant than old modes.  They can't just fix standards support overnight, or else the web will be broken for all people who use IE.  I'm not sure what they'll do:  these compatibility flags could divide the IE codebase such that the old cruft never gets updates and develops security bugs and general bitrot.  It might lead to a slight reduction in the quality of the browser if there are too many conditional interpretation flags. 

For what it's worth, a mature product like IE which is a platform for a wide variety of applications which have been tailored to its particular quirks cannot change very often.  Similar things go for the Windows Window Manager.  Too much stuff relies on the DWM working flawlessly, and I'm sure that team has not yet spent the time to solidify their code against unchecked third party callers who can pass in all kinds of random junk and break the whole Windows desktop.  You simply can't rely on third parties to do it right when it comes to affecting all other running applications, until you can define an interface which prevents them from doing anything too bad.  (Won't you love to see the new generation of Ad-ware that features integration with the Window Manager itself?  Pixel-shaded adrotators in every window would be glorious, no?)