Maybe it was an oversight.
Could someone check if any Shapeshifter (or fey) gains an Extraordinary Shifting Ability? If yes, than they might have feared a loophole.
But the loophole is, in a limited way, there - look at the Mimic (an Abberation, if memory serves well), if you shift into this form, you can use its extra-ordinary ability to shift into any kind of object, within some (maybe severe) size limitations, and won`t have to pay any of your daily wildshapes for it.
(Okay, it`s not really "powerful", but it might be of some limited use...)
Mustrum Ridcully