This is a complicated issue and I'm no lawyer, so I don't claim to have all the answers. I do however believe that like anything else, the problem can be approached with common sense.
Lets start at the beginning.
The problem now. The other ten percent share belongs primarily to Apple, Linux and various other versions of Unix as well as a variety of upstarts led most noticeably by Be. When an application developer looks for a market to sell their products they must as a matter of business look to the overwhelming numerical advantage of Windows as their primary target, often leaving truly innovative OS developers wallowing in an ocean devoid of software to run on their systems. Worse still, application developers themselves face the Microsoft menace. Because Microsoft the application developer, is also the Microsoft the OS developer, it controls the code that other application developers must use to create their wares.