Blizz has to balance the price, so they make the entry level cheap enough for new players not to get overwhelmed, but not so cheap that spammers can just buy vanilla accts. There will most definately be a new battlechest, hopefully for $40 including Vanilla, BC and WotLK, and Cata will be in its new box.

I always thought it was a shame that there wasn't a single, all-inclusive box for new players. IMO all there needs to be is the newest expansion only, for existing players to upgrade, and a box with everything all together, so one box, one purchase is all you need to start from scratch. I guess its cheaper to manufacture and inventory 2 boxes. Oh well.