According to Apple, once enabled, you will be able to tether your iPhone to a PC or Mac either via
Not allowing iPhone-iPad tethering doesn't seem to be an oversight. It seems like a carefully planned decision on Apple's part to keep AT&T happy. It is very possible for Apple to make tethering work via a software update perhaps along with a new connection cable, but I really don't see that happening since it will interfere with AT&T's iPad cellular connection plan pricing while maintaining the value of charging an extra $130 for a 3G-enabled iPad.
I understand that this is a business decision and that making as much money as possible warms shareholders' hearts, but to me this premeditated decision is dirty pool and another good reason to Jailbreak your iPhone.