Linux offers basic functionality that most people would be perfect with unless they are gamers, or a business big enough to require some formal support, but then we have companies like Red Hat that provide support for their OS, ... then the question becomes what is it that MS has that people still want to stick with it? The answer I think is:
Applications for business ranging from Office to custom made software for companies...
Games... that is going to change with Steam OS...
Don't see any home users that can't use Linux as Windows replacement... email, videos music, web... all free...
Business sticking with software made for Windows... I guess that's it... Active Directory? Not very cost efficient to migrate to other solutions, plus end user training.
The problem now is that people working in those companies are using other devices or OS's at home, then over time, they find out that they like or don't need Windows but only for work... MS is losing ground because of other OSs being good enough (Linux) or better Marketing (Apple) (What is so good about Mac OS? Looks pretty and then?) Anyway, after all these users switching to other OS's and being satisfied with them, they start questioning MS predominance for everything (like myself).
Many choices out there, one can be really picky on how we want our desktops to look like, functionality wise, all are the same, web mail, videos, music, word processing.
What I found out about Linux is that even though new releases are very complete and stable, they are not fine tuned, so there's room for improvement and with that comes the tinkering and issues that are difficult to fix. It's discouraging to know, for example, that the my graphics card could run better but installing and fixing drivers can really be time consuming, at least for now, until better documentation becomes available or versions between the same distro start being more consistent.
MS wants to spread its OS's as much as they can so people can focus again on the easy way of running everything in a familiar way.... making it as fun and pretty as possible like Apple did with OS X, but not as complicated or costly,buggy, (Vista,8) that everybody starts looking at free, stable, familiar alternatives.