The most popular camera on Flickr: the iPhone 4S. Not just the most popular cameraphone—the most popular camera. The second most popular at the moment? The iPhone 4.
Cameras brands, in order of popularity on Flickr: Canon, Nikon, Apple, …, Samsung, HTC, …, Nokia, Kodak, Motorola …
Cameraphone popularity, in order: iPhone 4S, iPhone 4, iPhone 5, iPhone 3GS, Samsung Galaxy S II.
Source: http://www.flickr.com/cameras/
Perhaps they're causing some bias in these numbers today by not pushing the Android app, and some more bias by not reporting Android phones as a group, but given the data they have, I'm not surprised they push the iOS app over the Android version. It looks like their user base is very heavily biased towards the iPhone.
Taking this a step further, perhaps Flicker is trying to align more with the iPhone/Apple brand than the Google (Picassa/+) brand.
I love my galaxy note to pieces but I still take photos on my iphone!
Google's inability to get carriers & vendors to be serious platform maintainers is the best thing which happened to Apple.