They say the Android Play store has just as many apps as iOS, but that iOS apps bring in over 4 times the amount of daily revenue over Android apps. There are other analytics by Flurry sited as well, and in general it highlights that you can make more money as an iOS developer than an Android developer, at least for now...
My thoughts are, while I think Android is going to eventually grow bigger than iOS in terms of overall spread of the OS itself 'Android', I do think it's important to point out that that growth can also be a dagger because of the device and OS sprawl occurring.
As reported here a few weeks ago, Google is already struggling with the device sprawl and trying to keep everything close to the same OS version. As a developer, knowing your 'target' is a big part of the battle and that is one huge benefit iOS has going over Android - much less device and OS sprawl and a somewhat predictable market.
Another important note, is some of the numbers when talking about Android vs. iOS need to be quantified. For example, with Android just about 'anything goes' in their market. So silly apps abound, whereas iOS is much more strict and requires developers to create apps that accent the device features and overall functionally. It's a bit like comparing diamonds to coal.
In addition, Android has always lacked one key element for drawing an audience and that is a solid in-app purchase. True they now have an in-app billing process but it doesn't necessarily work to the developers favor.
Lastly, why would they want to move away from something they know? What I mean is, if you believe there will be an 'exit' from Apple that is to also believe developers will abandoned their programming talents with regards to the Objective C, or similar iOS languages. I don't see that happening.
On more point I will also add. That is that there are several cross-platform SDK's that are well used and allow developers to target many platforms at once, iOS, Android, Amazon, etc. The stronger these grow the more they will be used which further diminishes the battle of the markets for developers. Having a silver bullet app build that is ready for several markets at once is the way to go!
Perhaps as Android grows it will also mature, and with that will likely come a more stable environment for developers to target. I don't know when that day will arrive but I do not think developers are going to abandoned the iOS market anytime soon.