As far as I seen there seems to be a lot of character classes but whats really important is how much those classes differ. Theres no point in having a dozen various classes if half of them do the same thing.
My question is, how long was that game in your Q? I had it in there for a while now, but I havent gotten a copy shipped to me.
But as for your question, they probably just let you buy the older games, not the newers ones.