A lot of people have issues with Apple's control over iPhone OS, but I honestly feel like it's more of a principle-based issue, not an actual utility-based issue. If it were utility-based, those people would just jailbreak, like I do. I have no problem with Apple maintaining strong control over its operating system, they are merely ensuring the best possible user experience for their consumers, both advanced and ... less advanced.
Much of the control issues have to do with AT&T as well. The banning of certain 3G-based services is to provide a better network connectivity experience for all iPhone customers, as the USA is densely populated and very much in love with iPhone OS devices.
Let me put it this way, if all the nerds with iPhones are tethering, Heidi is going to have a hard time uploading her photos to facebook, and she's going to get frustrated with her iPhone and with her service from AT&T. AT&T's network was already not prepared for the iPhone (and still isn't), there's no reason to make matters worse for everyone on the network.