So playing a character with a 20 Int or one with 8 Int shouldn't affect you? Really? So someone below average intelligence or one of the smartest people in the land should speak the same, both use the same vocabulary, etc, etc...
Really?
Intelligence sums up mnemonic ability, reasoning, and learning ability. Maybe the PC reasons just fine, but has a severe learning disability, hampering their intelligence score.
My low intelligence score PC's usually get a headache when they try to read and don't much like book learning.
Someone with a low charisma might be well spoken and ugly. Or they might be very attractive, but no one likes them because they haven't bothered to learn how to relate to people. My low Charisma PC's are jerks.
Someone with low wisdom may or may not exercise poor judgement, but they might or might not have great willpower. Most of my low Wisdom PC's exercise poor judgement, or are very impulsive.
It's really up to the player I guess, generally I attribute a low score in one of these to a deficiency in one of the areas.