The development cost of "moon" I would think was tiny compared to GTA CW. GTA games are not made to make a little profit, it is the one huge franchise 2K has and they expect each game to make huge amounts of profit.
The PSP GTA games have sold 3+ million yet have ignored the console for some time now, that pretty much shows just how much profit 2K expect from each GTA game. Rest assured R* will not be happy with these sales, sure they will be praying that the DS legs kick in a big way but right now for a GTA game? Rubbish sales, simple as that.
Edit - Looking at how Moon is selling I would indeed think the man would be pleased with 60k.