[OriginalSyn]

That's because Amazon locked Rovio into an exclusive deal, you could only get the Ad free version from the Amazon App Store.

[OriginalSyn]

Proof for the downvoter: http://www.amazon.com/Rovio-Mobile-Angry-Birds/dp/B004SBQGHS...

and

http://phandroid.com/2011/03/30/after-brief-amazon-exclusivi...