Really? I thought that the design component and ability count functions didn't work when used in component requirement fields. Hmm... wonder if Aaron changed something recently and didn't tell us. Awesome.
That method has a slight drawback, in that if a player doesn't know about the mutual exclusivity, and doesn't pay too close attention to the reqs list in the component descriptions, they won't know what is going on when they try to add the second component. This might not matter so much, but is worth consideration.