Well, they didn't try, even back before all the antitrust rulings, so what makes YOU think they would?
They did not try, because they either did not think of it or could not figure out how to do it.
And they would because that is how MS works.
Also, as has been mentioned if they did try, they'd get sued for antitrust violations. Microsoft doesn't even include a lot of their in-house application suites (like Live Essentials) with the OS because they'd get sued for it...let alone blocking competing products.
If MS had things set up properly (which they don't), they would not have been problems with anti-trust.
For example, from day one, Apple's developer agreement stated that an App could not duplicate a feature already in the OS and could not alter the way the hard buttons operated. So, banning Apps that duplicate features or modify the hard buttons should not be a surprise (or news-worthy).
As has been mentioned (and not disputed), MS had "borrowed" ideas and features from developers. Anti-virus is a good recent example.
MS cannot ban applications because that is not how the Windows ecosystem is set up (though MS probably wish it was). The iOS system, from the ground up, always required getting past Apple's velvet rope.
AGAIN, I am not defending Apple's actions. I am just pointing out that Apple's actions are not worthy of such a thread since it is such a widespread, well-known way of doing business in the industry.
MotionMan