Power Specializing

I was just reading someone else's CoH blog tonight. He was complaining about how at the mid-levels you're sometimes forced to take a power you really don't want. I've been there myself. It brought me back to a question I had some time back... Why can't you take a power more than one time? If I don't want to take Crippling Ax Kick for my martial arts scrapper, why can't I take Crane Kick a 2nd time? It's obviously less "powerful" (from a game mechanics aspect) than CAK as it falls lower on the power "heirarchy," so at first glance taking it twice wouldn't appear to be game unbalancing. It would also contribute greatly to character variety. I'm sure someone at Cryptic gave this some thought at some point, but I'd like to know what their reasoning was for not allowing it.