Of course the DS does not have comparable graphics to the PSP, but that has nothing to do with the DS's storage capabilities. The largest DS game, storage wise, was Archaic Sealed Heat, which had almost
every single cutscene, attack and spell animation, and battle sequence in the entire game as prerendered CGI scenes
Gametrailers.com - ASH: Archaic Sealed Heat - Dragon Confrontation Scene
^That is what almost every single cutscene in ASH was, that quality CGI.
And you want to know something interesting? ASH only used 1/2 of the largest DS cartridge available for development on the DS. As in, there hasn't been a DS game
yet that has maxed out the DS cartridges' space.
And no, Dragon Quest Monster Joker didn't come close, DQM:J was 1/3rd the size of ASH. The largest DS game Square-Enix has developed was their spectacularly well done remake of Final Fantasy IV, which too was smaller than ASH.
Final Fantasy IV, Archaic Sealed Heat, and Dragon Quest Monster: Joker could
all actually fit on a single DS cartridge, and it would just about meet the DS's storage capacity limit.