Originally Posted by Sylph1
It's because during a match, AP or AD enabled champions have the option of adapting to the opposing team. If the other team has high magic defense, you can go AD. If they have high armor, you can go AP. I guess it's a way of saying, this is an assassin and can be built with a viable damage output regardless of the situation.
I'm pretty sure you're at least in part wrong there. I'm speaking of the abilities which benefit from AD or AP. No matter which one they use, they still deal magic damage (in general).
Also, why should some champs have the option of adapting to the other team by going AD or AP while the vast majority do not?
What I'm getting at here is Ability Power is just that.. power for your abilities. It seems to me that because the available items did not allow some champs to get the AD they needed as well as have effective abilities, they made the abilities use their AD instead of just making items which allowed this to be possible.