Similarly, Microsoft would likely be a dominant player in the chat space today if they hadn't rebranded and renamed MSN Messenger several times and then abandoned it altogether.
MSN Messenger was frickin awesome. You could draw pictures into the chat window. You could play a game of checkers while you chatted. It had a thriving ecosystem of apps and plugins. Everyone I knew used MSN Messenger... and then one day, Microsoft just said screw it, everyone can move to slow and clunky Skype... and that was the end of it.
Hell, ICQ might still be around if AOL had put more development resources into it.
The chat space is so bloody fragmented now, but it has nothing to do with Apple. Any one of the above mentioned companies could be killing it in this space if they hadn't pissed away what they had.