Quality control is another word for "high barrier to entry", and especially with their market position, being rejected by Steam for some arbitrary reason would effectively kill your project.
Not only should they not restrict the ability to sell your games there without a concrete reason; they shouldn't be permitted to do so. A company with that much influence shouldn't be allowed to be a gatekeeper of what constitutes a "good" game.
Their review system and strong return policy are more than enough.