Japanese devs are simply all on the DS, most titles on the PS3/360 are geared at trying to break into the western market, games that aren't in that group MH and DQ have had no trouble moving on to the Wii. You also have to factor in the blue ocean strategy here, many devs are still too used to the red ocean approach that we've been used to since the NES and will cling to it until they're forced to try and adapt to the blue ocean approach properly as in actually being competitive as well as putting in effort rather then just releasing a game any how of debatable quality. Think of it as fish in a stream that's gradually drying up and rather then move to the ocean while they still can many are staying put.
Many try to complain it's hard to make money against Nintendo but I think it's an excuse for them to explain why they don't even try.
