Nope! That's the beauty of Android. Even though there is a AppStore equivalent, you can download an app from anywhere. Plus, it's programmed in Java, so you don't have to worry about all that mundane stuff like garbage collection (just at the cost of speed).
Don't mean to insult the iPhone. It is a great platform too.
EDIT: A lot of people have been noting that the iPhone APIs are not restrictive, but rather the approval process is. This is true, however the iPhone's APIs are still somewhat limited, in the way of low level hardware access, backgrounding (only notifications in 3.0), etc.
iPhone 3.0 is a step in the right direction, but there is some work left to do.
Also, have you considered making JB iPhone software? I'm not sure of it's market share, but I do know of a lot of people with Jailbroken devices.
EDIT: I have read in some more posts on similar questions that Android's Java can slow things down due to the Garbage Collector. Just something to watch out for.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…