I agree its a gamble and its a relatively new thing (last 10-15 years). These big budget comic book adaptations brought it on and it seems par for the course these days if you've got a big comic book/scifi/fantasy movie coming out then you'll have not only the usual figures that you'd typically sell in Target or whatever but also high end stuff.
I think its a bad idea personally, a lot of these figs end up in clearance sales coz the movies sucked and no one wants em. How long did Superman Returns stuff linger on shelves? GL stuff?
It is a high-risk, high-reward gamble. If the movie is a huge success,the company gets the first mover advantage and will be able to make a lot of money. If the movie sucks, they end up with a large amount of inventory. I'm sure that these companies have analyzed the potential scenarios to death and are taking a calculated risk.