But let's suppose people really do buy good games with poor graphics. Suppose the next Zelda just totally sucked but was perfect in every cosmetic category, and as a result it bombed. Does that mean Miyamoto should start talking to the other 100 members of his team like the graphic designer or the music composer on how to design a better Zelda game? No it just means they need someone to replace Miyamoto as the head guy and keep the guys who managed to do the cosemetic stuff perfecetly. How 'fun' the next Zelda is will almost certainly depend on what Miyamoto did. Likewise Metal Gear will depend on Kojima for all its 'fun'. Now beyond those two I don't know anyone famous enough to tie to a franchise, but you can be assure there is one such individual that is responsible for the bulk of any game's (or lack thereof) fun factor.
I don't understand why people hate great graphics. Graphics and fun are complementary and managed by totally different entities. If one failed it's not because the other is hogging all the resources. Miyamoto probably wouldn't even be very good at cranking out polygons, just like surely they do not ask the graphic designers how to make the Zelda engine. If the next Zelda game has stick figure graphics it doesn't mean that the fun factor must go up because all these guys who should be doing graphics are helping design the games (in fact that will almost certainly make the game a lot worse). If the next Zelda game had great graphics it is not because Nintendo forced Miyamoto to learn how to design computer graphics instead of doing his normal job.