Microsoft's position seems to be to make their newest OS run the web best. Nothing wrong with that; and they've ensured a vibrant application ecosystem for XP that has led to many browser vendors supporting that OS well. XP users aren't exactly left high and dry.
Also, it's naive to think that everyone else's interests are merely to make a better browser: Google does it to get people spending more time on the internet under the assumption that they'll use Google to search and click on their ads.
Business arguments aside, I really wish they would support IE9 on XP. If indeed IE9 has better web standards support than its predecessors, I, as a web developer, want IE users to switch.
It's hard enough to convince users to upgrade their browser. If you ALSO have to convince them to upgrade their OS, there's basically 0 chance of that happening.
I'm not saying MS is or isn't making the right decision for their business. I'm just saying that IE9 is a lot less exciting for web developers if it's got this big roadblock to adoption.
