The way i see it, Sony's prime difference is that their western branch seems to be approaching first party development like a movie studio. They build a brand and if its hot, they put out more products in the short-run (i.e. the generation) but then put the brand aside in the long run, to possibly return or possibly not (see: Jak in Move Heroes), whereas you see their Japanese studios trying to build longer-term brands, though SCEJ hasn't really made any breakout hits sans Gran Turismo, you see some of their old favorites recur every so often, namely Ape Escape and Hot Shots
Nintendo builds icons, but the problem being the icons crowd out the potentiality for new IPs. I mean, hell, we didn't see a home-console Starfox or F-Zero this generation, and that's because Nintendo's running too many medium-sized icon brands under their top-tier or prestige icon brands (Mario, Pokemon and Kirby falling into the top tier, with Wii ____ there now too, and Zelda and Metroid in the prestige column), more than they have resources to deal with, let alone make new studios
Sony makes all these new IPs because they toss aside their old ones, which some people frame as a bad thing (and given that none of these new IPs never reach Nintendo or Halo levels of success, it could very well be a bad thing objectively), but primarily i think it's a difference in attitude. Nintendo fails to make new IPs because there's more demand for their big brands than they can handle as it is, let alone if they really tried to branch out creatively, and because its easier to cushion new ideas by transferring older characters into them (seen with Kirby's Epic Yarn and Kid Icarus Uprising, both of which were new IPs in the concept stage of development)

Monster Hunter: pissing me off since 2010.









