I think this is why Instagram didn't make Android a priority right off the bat.
According to an article on Techcrunch, the Android version of the app will be ready real soon now.
Apple on the other hand has almost as many users and you can test your app with just a few phones. As an individual who has his old 3GS, a new iPhone 4 and an iPad I literally have everything I need to test an iOS app.
If Google were smart they'd collect all the various Android devices and offer a testing service to developers. If they charged for it they'd get a new profit stream while simultaneously making it easier for developers to create Android apps.
I say this as a devoted Android user. Nobody has come anywhere close to Apple's marketing prowess, and until that day comes it makes absolute sense to build for the iPhone first. This is the same approach the fashion world uses for clothes, and it's a proven model.
While I love Android, it's very much a case of a grandmother trying to dress like she's 20 again - it's not attractive, and while the parts still function, there's really no reason to tap it when the hottest chick in the room is staring right at you.
Look at Angry Birds (edge case, not exactly a great example) and how moving to Android caused them to move to advertising, which ended up making them more money and moving that model to the iPhone.
I think it is bad that there is this mentality that there is iPhone and then there are smart phones. The iPhone shouldn't get any special treatment, because at the end of the day it provides the same thing most any Android phone will.
Now that I realized that this has nothing to do with the OP, I have to say that it is good that Instagram has an API.