As for the other things, I've been wondering, too!
> Why are they so small?
Probably because they're afraid people accidentally touch them? I think if Apple dares to make them this big, that's probably an irrational fear.
>Why are they not centered?
After a _long_ time thinking of it, I got an idea: Maybe they're centered on the space bar to be between your hands when typing? That, however, would also mean that they acknowledge that you're usually holding your hands off-center to reach around the number pad. Has anyone used a laptop number pad in the past 20 years? I agree that they should go in favor of a more sensible overall layout.