Big players don't fragment
Before IBM standardised the whole world on IBM PC clones there was huge diversity in the types of PC architectures that were available. There was no real OS, so software authors really suffered trying to make software that could run on a reasonable cross section of machines. There was MS-DOS (and others), but you had to bypass MSDOS and do direct hardware access to get anything like reasonable performance. Since all the different machines had diferent hardware, it was very difficult to write apps that worked well on all machines (or even a few common ones). Thus, it was really IBM and not MS that kicked off the "PC revolution".
There are quite a few Linux phone stacks but until one of these emerges ad the de-facto standard it will be hell to write phone apps. Writing for 5 or more different phone environments is just far too impractical. Google is a big enough player to provide a standardising influence. On course, Google could have just endorsed an existing environment but they have added some very interesting stuff in Android.