Microsoft has traditionally made software, and rebranded things like mice and small peripherals. They only 'recently' got into the xbox, but that was different for it was a game system.
Now, with them being a computer dealer now, where does that leave Dell, HP, and other manufacturers?
It's high enough make the competition (Dell, HP, etc) put out good products that won't tarnish the new Windows platform image. But not so high as to make third parties not want to bother competing.
This was a problem with early Android. There were so many poor devices that the entire Android brand was hurt (but since recovered).
I believe the major difference is that Microsoft has entered the computer manufacturers arena as a 1st tier manufacturer. Everybody else is now tier 2. And this leads to problems with monopolies and vertical integration.