He says he doesn't want to get into it, or does he?
For all of our deep abiding faith in the marketing genius of the Weinstein Bros, they simply don't have the tools they once had. The theory was that QT & Rodriguez were living franchises ... and to some degree they are. The same way $24 million was pretty damned good for a Kevin Smith Clerks sequel, $30 million to $40 million domestic gross for a grindhouse homage seems pretty reasonable. Unfortunately, the movie they made was too expensive for that number to be ok.
Again, a popular refrain: movies are too expensive to make, and if you're going to do something risky, keep your costs down.
300 hit the jackpot because it both kept costs low and had a fantastic marketing campaign - double bonus.
On a slightly separate topic, I think it's interesting that the last two movies that "disappointed" box office pundits were Snakes on a Plane and now, Grindhouse. Perhaps there actually isn't a broad audience for tongue-in-cheek movies that say, "we made this movie badly on purpose."