You are unable to trade the most powerful items on the AH because the LE team wants players to engage with the world in order to find those items rather than buying everything from other players. I think this is a great idea.
It sounds like players can “gift” any item to somebody who has been on their friends list for a “reasonable amount of time”. A possible loophole that immediately comes to mind is that a large group of players could add each other as “friends” in order to exploit that system. Or, a player could simply “friend” a player associated with a real money trading site which would then allow them to buy or sell items using real money.
Perhaps LE should also require players to spend time playing together in order to be able to trade the best items in the game, such as a running average of 2 hours per week over the past 4 weeks.