Do All Free Apps Contain Ads?

[BobHelms]

New to the iPad 2 world. I've noticed that free apps contain ads. "Sundry Notes" contains an elaborate one for AT&T. Is this a common practice in the iOS development world?
Bob Helms

 

[Tim SPRACKLEN]

There are many free apps that don't contain ads -

NASA app
BBC iPlayer

to name just two...

Tim