I just noticed the average human had 13 in his stats. I've always had 10-11 in mind in reference to 3d6 rolls.

Is read/write linked to a stat? (if so when can you not read/write?)

You're assumed to be able to read/write if you're of any class but a barbarian, though even they can become literate through multi-classing. Reading/writing does have a stat in normal DnD, but not here in NWN (that I know of). As to the average stats, 'normal' people get the 10-11 range, but since we're 'heroic' characters, we sit slightly about average in the 12-14 range. 8)