There was no Sorcerer class in 2nd edition rules so Bioware "stole" the kit from 3rd edition(which you may well know). In 3rd edition the sorcerers main stat was charisma, however this isn't implemented in BG2.
Intelligence only affects MAGES writing scrolls to there spell book so again because Sorcerers don't write spells intelligence isn't a key stat for them.
So basically sorcerers in BG2 have NO main stat.
However you'll want:
good dex for the armour class bonus(if your in a party it may help but, if your solo and playing properly you should never get hit)
16 con for the highest possible hit points
Decent itelligence so you can cast spells from scrolls.
18 wisdom for the wish spell.
Have fun nuking everyone into oblivion!
