From that same chart I could say developer interest in iOS is on the decline
Yea.... except you see percentages. The share is shown, not the number. It could be that the growth of iOS development is just slower than that of Android. As many pointed out: The revenue is important for developers - simply, most of them live off it. So, you either have a good free app where people touch your banners or links often enough so you make money, or you get your app to be bought for real money in the first place.
Now, if your App at the AppStore (Apple, for those who don't know

) brings in revenue, you might just stick with it and make it better, get some in-app purchaise going if possible, etc. and you won't count for "new releases" anymore in the above statistic.
Others mentioned it: Android is all about free and mass. If you are the same developer and your app just does so-so, you gotta get the next app onto the bandwagon so you keep getting money. Updates etc. might not accumulate the revenue like in iOS, so they are less attractive. Besides, having to deal with "screen size multiplied by Android versions running" - or a gazillion possible configurations - your App might be buggy on a lot of devices and then you just keep bugfixing (not even mentioning that the bugfix could create a malfunction on a device it worked well with before the "fix").
Talking about that: How many devices do you have to own as a dev to make sure it works vs. developing on iOS? iPhones:
1. original
2. 3g
3. 3GS
4. 4
5. 4LTE
6. 4S
(and some iPod Touch - but same hardware and screen sizes)
So, you are at less than 20 devices for handheld. Now, just look how many different ones come out each month for Android. I can imagine, it's a nightmare...