3rd parties won't come because Nintendo doesn't feel the need to relate with them, specially in the west since third party support for Nintendo consoles have been great in Japan, but they're too autistic to try the same deals that landed them Monster Hunter Tri or Dragon Quest, in the west. Quite honestly they don't seem to think too highly of us, all they have is a few very controlled studios.
This then extends to public relations with the western gaming press which then extends to the hardcore gaming community perception of Nintendo consoles.
Another reason, that I agree with you, is the graphics. Ever since the bit wars, video games have always been easily rated by their graphics, it's the most noticeable change between iterations of the same franchise and can easily hide a game's shortcomings. Developers can more easily build hype around their game with a pretty new face than around their new innovative mechanics. It is just human nature, everybody likes graphics and that's something developers can easily offer on powerful machines, on the other hand, new innovative game mechanics aren't perceptible in screenshots and there's no realistic way for every developer to come out with one for their games.