I don't get the $20 tether "unlock" fee or why Apple won't allow iPad tethering
Apple should allow this feature for people that own both iPhones and iPads, but don't necessarily have a need for the dedicated and more expensive 3G model. Some people don't have a need for 3G data on iPad regularly, but may need 3G data for short periods of time, randomly. Perhaps once or twice every other month.
Let's just imagine that iPad had launched in a world where tethering was available on iPhone/AT&T with the current data caps. For the type of user described above, to not allow it, makes little sense.
To me, it seems that whatever task you would normally have performed on your iPhone, would transfer to your iPad (e.g. reviewing, revising and uploading a file a colleague just sent you on Dropbox) while you're in a taxi, or on a construction site. Since the task is simply transfering from one machine to another, it's not as if you're suddenly using more data. You are simply accessing it on a bigger screen, within an app that's offering enhanced functionality beyond the iPhone version. Therefore it should be free, especially in light of the fact that their current $20 tether fee gives you NOTHING. No extra data bucket. NOTHING.
Putting the iPhone into hotspot/tether mode could be enabled with a simple toggle. Perhaps seamlessly by having iPad tell iPhone it needs a data connection. It adds value to the iPhone/iPad ecosystem and fits into Apple's design philosophy of simplicity, elegance, and ease.
How AT&T loses in any meaningful way....I don't see. The data caps are in place. If you abuse, you pay.
Some say they're a business and have a right to charge for this. Fine they're a company and have the right to charge (even though they're charging for nothing), well, they could offer a small opt in fee monthly for people that MAY need to use iPhone 3G data on their iPad once in a while.
People are going to use MyWi "for free" anyway. They might as well get what money they can, by offering a reasonable option.