Aye, Rovio made Angry Birds – they nearly went bankrupt, but fortunately for them Angry Birds (something like their 58th iOS game) made it big. It’s now had over 1 billion downloads across the different variations (Angry Birds Rio, etc) and formats.
They released it on Android as a free version with ads, as piracy is so rife that a lot of developers choose to release paid versions on iOS and free-to-play (free to download and play, but with adverts/more dependent on in-app purchases) versions on Android.
As it currently stands with Smartphones, iOS takes up 23% of the marketshare, Android takes 59%, and the remaining 18% is split between Blackberry, Symbian and Windows. Those versions are likely to be more expensive due to the cost of porting them to a different format, but with a smaller market.