Microsoft got lucky
Since DRI passed up the chance to make an OS for IBM, Microsoft got the chance and took it. Neither IBM nor Microsoft knew that the IBM PC would take off so big, or how big the Microcomputer market would get.
Boom! The market grew, as did Microsoft. Compaq and others made clones of the IBM PC, and Intel sold lots of chips to IBM-wannabes. Microsoft made an OEM out of anyone that wanted to be like IBM, but they had to follow Microsoft's rules.
Eventually Microsoft learned that it had to market and distribute its software. Then things changed. Maybe around this time they learned how to strong-arm OEMs and bundle software? They dropped Xenix for MS-DOS, and later bundled MS-DOS and Windows. Then they learned that by bundling MS-Works and MS-Office with OEM versions of Windows, that they could take out competitors like Wordperfect and Lotus. They got lucky and it worked, it worked all too well. Now the DOJ came down hard on them, so are the US States and other governments as well as class-action lawsuits. At this point, Microsoft wasn't so lucky anymore, but still had an iron grip on the market.
But as for the future of Microsoft? Who knows? If they can no longer bundle software, get split apart, or get limited in what they can do, they may not be the powerhouse that they once were. The market can change, remember that the market once changed away from standards like CP/M, Apple //, MS-DOS and others.
"I can see if I want anything done right around here, I'll have to do it myself!" Moe Howard