I think Capcom, and in this case, Konami, are remaking several games for the PSP because if they do them for the DS, they'll feel obligated to use the two screens, the touch screen, or the microphone. I guess it's "simpler" to just make it look nicer. Come on, the second screen could be the map, which would be handy if SotN was feasible. But at least the DS has new Castlevania games...
Those are two good games, though. I still have to finish playing through RoB.