When I first read about NetShare, an application for the iPhone, it actually gave me a reason to want to buy a 3G Apple iPhone to add to my collection.
Instead of pulling the app, Apple and the carriers should simply come up with a pricing model for tethering.
The problem though is not as much Apple's but it impacts them. For AT&T here in the USA to keep up with the data demand it will cost reportedly from well informed sources close to some $7 billion dollars to double the capacity of their 3G network. By reducing tethering AT&T is able to grow their network and add users in a structured manner. But the unanticipated success of the iPhone, which like Blackberry requires a data plan to work, means the network is being stretched and likely can't handle too many users being added to fast. That's one reason why the "illusion" that we're seeing of demand each day for the phones is likely happening. Apple and AT&T want to keep the interest going around the iPhone.