And where do you draw the line? Do you need to buy Claws for a wereraven in order to actually have them even though you are a bird, etc. Or a beak. Or a trunk for were-elephant (ok that's a joke but you get the meaning I hope).
I've interpreted it more like this:
If you use beast change to turn yourself into an animal, you are in the shape of that animal, no questions asked. In your case, you are a raven, a tiny bird with wings, claws and a beak. Can you use them effectively? Absolutely not.
To be able to use your wings, you need the wings power, otherwise, they are decorative.
If you want to inflict more damage in physical combat because of your beak and claws, you need the claws power. You could get by without it and use your claws for non-combat stuff, but the damage bonus would be denied.
You want to use the fact that you are tiny to your advantage? Get the diminutive size power. Otherwise you are too set into your human ways of thinking and are not able to use your new size to your advantage.
By the way, a were raven with maxed out stealth is awesome
