Microsoft is king because
- IBM clones were cheap
- Bootlegging their operating system (and products) was easy
Every home-built, computer-show PC with a bootlegged copy of DOS or Win 3.x was part of Microsoft's success story. Anyone remember the TRS-80? The Amiga? Apple was hanging on by it's fingernails and Linux was a home-brew OS that data center and academic people played with. After computer technology was mature Microsoft could enforce product licensing better - game, set match. They certainly now aren't going to lose at the tablet game, they're to big for that. If they do get out of tablets I'd be concerned about tablets.