how often do people play the INT of the character or it's WIS. Most of the time they don't. DM's dont' tend to enforce that either. They also don't tend to let players say "Hey my guy is really smart can't I roll to figure out this riddle?"
I think cha is like int or will or wis or whatever. The only reason STR and the like make sense is because there are combat rules that require it. If you want to pretend to be another person(or whatever) then that person should have a part of them that is their power of personality that is reflected on the sheet. As to good roleplaying being trumped by a die roll. I've seen high dex and str guys fail something they should have easily done.
As for dice rolls saving time, I think there are better options involving limited talk.-sometimes it's nice to have a system to make it so it's not just on the fly as it were.
Awareness-As to why it's not perception. It's because magic isn't something that is seen, it's felt. Perception sees things in this world. System creation has a lot to do with world creation.