Microsoft
How much innovation has been made possible by putting cheap computers in the hands of just about everyone who wants one?
Microsoft's monopoly has been largely earned, and the rest of it has been due to its competitors' screwing up.
"In 1989 I went to all the applications publishers and asked them to write applications for Microsoft Windows. And they wouldn't do it. So I went to the Microsoft Applications Group, and they didn't have that option..."
--Bill Gates, in the mid-90's.