Well, developers write the applications that the masses use. The strategy is a relic from IE's days as the only significant force in browser marketshare. Microsoft wants you to consider that almost all of your users will be using IE. They want you to see that and then decide that IE is the only browser you can afford to support. And then everyone is stuck with Windows, and it self-perpetuates, because users need IE to go to the websites they like, and then more users are using IE/Windows. You see? That's why IE features are always "broken" and half-implemented. If HTML etc. worked as defined in IE, people could abandon IE at will.

IE is still the dominant browser on most sites, so maybe that strategy still has value. It's becoming less and less significant as OS X (which comes with Safari by default) and Firefox gain marketshare. I wonder when they'll decide they need to reconsider; IE has certainly cost them a lot so far, legally.