[Crazy Jetty]

actually... there is a potentially important nugget in that last answer I've never seen any of us consider before. Fitting them into the pricepoints retailers are demanding.

This is a very important aspect too. I'm in no way defending mattel at all, when hasbro has been able to manage it themselves, but this is definately making me look at this from a new angle.
We can only assume that Mattel's production runs are quite a bit lower than Hasbro's. We all know that means smaller profit margin per unit sold, and higher production costs per unit, because they don't have as much product to spred the costs out across.
So, it looks like it boils down to this: Hasbro has more product sold in more places to be able to meet the price point the retailers are demanding, with a figure that has as many moving parts as fans are demanding. Mattel does not.

Again, not defending Mattel, but that makes this make a whole lot more sense.