Competitor? Windows is still >85% of desktop use or thereabouts - you can buy an expensive mac or you can go to hell and try out linux; neither is really an alternative for many so they just accept what happens.
So why do they bother adding new features to Windows?
I'll answer my question: Companies make decisions on the margin. They don't care that they have 85% of the market. They want that next percentage point.
The users who might switch to or from competitors are precisely the "swing voters" they have to consider.
