Quote Originally Posted by Yora View Post
Because there is a percieved benefit in always having the same basic mechanic for everything. Roll d20, apply modifier, reach Target Number.

This is the one thing that I think d20 did perfectly. And the lack of it is what makes particularly AD&D so difficult to get into. A roll under system has exactly the same outcome as a DC 20 system and I think the benefit of having a single universal mechanic for everything by far outweighs anything that could be gained by introducing other mechanics for individual things.
I mostly agree with this. D&D doesn't really need subsystems, since at the end of the day it's only used for one thing.