1 million shipped in 20 days is good but it's nothing mind blowing that will make third-parties care about switch, and yes people buy nintendo consoles for mainly nintendo games, just look at how insane nintendo games are selling.
Nintendo gamers only buying nintendo games has always been false, certain type of games always sold well on nintendo platforms, even on wiiu. it's just thirdparty games are seldom a massive success, talking about big AAA games, nba 2k, fifa, COD, skrim, etc.
Gameplay > Graphics
Substance > Style
Art Direction > Realism