I don't remember sorcs being in 2nd edition at all, what I do remember from that edition though was that different classes gained XP for doing different, class specific things. So fighters got more XP from killing things, thieves from obtaining treasure and the like, wizards got theirs from casting/learning spells or creating magic items. If sorcs existed there they'd probably follow the wizard XP philosophy but get more XP for casting as they wouldn't be able to research spells, so D4 makes sense to me.
Baldurs Gate was based on 2nd Ed though and did have sorcs, they had no stat minimum reqs so you could theoretically pump that con higher than a wizard.