Yeah, Neopets is the only game I have played that has the multiple account allowance, though I have heard that I think Lionden allows for a side account linked to your main, though I have never played that game, so have no clue what is involved.

It is that reason why it always sort of mystified me when people go 'I had no clue multiple accounts weren't allowed! I haven't seen a game that didn't allow multiple accounts!' because just about every site I have played has had the no multiple account rules, and even none game sites often have this rule. (there are those that don't have this rule, but many of the ones I have seen tend to)