High PPI (300+) screen, why all in a sudden?

It's no secret that Apple likes to look for the newest technology out there, either buy the firm up or sign an exclusive contract with it, so that they can have a lead on the market for a while. What I'm having in mind is the Retina display.

I was really amazed by the quality of the Retina display when it was first introduced by Apple. The first time seeing it I really had my jaw dropped. I know many of you here are ready to troll. It's 3.5 inch, it's LCD, blah blah blah. I'm an Android user, and yes I love big screen. I was using an HTC Desire back then and I really liked the AMOLED screen on it despite the infamous Pentile. I guess many other Android fans out there were on the same boat, that we were looking for a quality screen with similar PPI. But NOTHING. For more than a year, nothing released on Android even came close. Yes, the first Atrix had a qHD display. But it was Pentile LCD, and having seen it in person, that screen had nothing to write home about. 

Now, right after the iPhone 4S was announced. All in a sudden, almost every screen manufacturer are releasing 720p screens, and every smartphone manufacturer can now make phones with high PPI screen. So what happened? Was there an exclusive contract to a piece of technology involved in making these high PPI screen just expired or something?