I'm really not trying to be an Apple apologist here, but, when you have a goodly chunk of the market, you sell virtually every device you can make and have insane earnings, marketshare isn't that big of a deal. As an Apple investor, I'd be thrilled if Apple had more of a % f the market, but what the heck, they do ok.
Licensing the OS would bring fragmentation to the platform, and although you don't see much about iOS fragmentation, it's there, there are essentially 3 versions of the iPhone now 3GS AT&T (GSM), iP4 AT&T (GSM), iP4 Verizon (CDMA) (plus if you add the varying amounts of memory in the devices, it complicates matters) and unless Apple starts using multiple radios in each phone (which has been rumored, but adds to the cost of each phone, something Apple hates to do). Look for them to kill the 3GS to help avoid fragmentation after the iP5 is released, and there are rumors of an inexpensive pre paid iPhone variant to be released soon.