[Dimensio]

You forgot another option:
Microsoft could incorporate GLPed code, never disclose that they are using GLPed code in violation of the license agreement and hope that they never get caught. Some suspect that they're already engaging in such activity.

[dheretic]

That's not an option. All it would take would be a disgruntled employee to get a CVS/SourceSafe copy of the lastest build's code on a CD-R and take it to the FBI and media. Gates and Balmer would be bankrupted by stockholder lawsuits because they would cost the company a cool several billion in revenue out of arrogance. It could also heavily drain that $40B that they have in reserve. Microsoft is well aware of the fact that in a company as large as their own, you cannot keep all employees happy all the time.