Errr, not quite. Steam has always let bad games on Steam backed by publishers. Moreover, "how did a game like Takedown make it onto the store?"--well, it's on XBLA as of next week and it's on PSN, isn't it? Aliens: Colonial Marines is on Steam. Rogue Warrior is on Steam. Tons of crap is on Steam. Nothing has changed at the publisher level, nothing has changed from Early Access. What has changed is the degree to which Indie titles can get on the store.
And the issue with that isn't that people are buying bad games and getting burnt. That would be "Steam needs quality control, and is squandering their reputation". Mostly people are not buying the garbage games, and mostly they're not buying the sort of semi-amateur games. Look at the concurrent players for any of those games--no one is playing them, no one is buying them. No one bought Revelations 2012. It came out and people immediately said "lol what a pile of shit".
The actual issue here is that when you have so many games that people can't tell good from bad, they avoid buying both and stick to safe titles. The worry is that someone who releases a great indie game gets no visibility, because he released the same day as 8 other titles. Someone who releases a great indie title faces an uphill battle to get noticed in a way that they didn't before.