Actually, they have a pretty strict policy of not including shovelware, to the point that the Microsoft Stores will, for a small fee, remove all the shovelware from a computer that they didn't even sell.
Microsoft CANNOT prevent licensees from loading any old crap they like. The US Justice Department sued Microsoft to establish this fact, and put a judge in oversight for the next decade.
The DoJ also prevented Microsoft from doing deals with the top 10 Windows OEMs, and compelled it to supply them all at the same price. This prevented Microsoft from doing any deals that would be unfavourable to any OEMs who chose to provide slow, badly-installed, crapware-filled systems.
Obviously this was a tremendous benefit to the American public, and to the rest of the world, which doesn't have a choice or a voice when the DoJ makes the rules.
There's nothing wrong with the idea in principle, it's just that OEMs have a bad habit of putting on too much stuff, and putting on stuff that nobody would want (or should have).
It's just all those installers (yes, I'm talking to you Adobe and Oracle) that do everything they can to trick you into installing "toolbars" and other crap.
