I don't think that's really true. Apple makes more money on hardware than anything else. The iTunes Store helps sell more iPods, not as much the other way around.
I think Apple's decision to require all iPhone apps be sold through the iTunes Store is partially a matter of control. If an app is malicious or misbehaves, they can easily pull it.
It might be true, tried to find the gross revenue per unit for an iPod (unable to). However, during my investigation I did find this interesting blog post.
http://daringfireball.net/2008/01/aapl_q1_2008
The author makes a few interesting notes about Apples Q1:
* Mac sales and iPhone sales were equal
* The gross revenue per iPod was $181
Also, apple made $808M on iTunes.
There is one interesting bit of foretelling in the post (written 5 months ago)
The market for third-party software for the iPhone and iPod Touch is already big, and I expect that by this time two years from now, there will be more iPhones/iPod Touches in use than Macs. (Imagine the unit sale numbers for a $199 iPhone two years from now.)
I think Apple's decision to require all iPhone apps be sold through the iTunes Store is partially a matter of control. If an app is malicious or misbehaves, they can easily pull it.