> Quoting and buying at their published bid/ask is precisely their function

I think he was making a little joke about this. He said:

   fill my buy orders at the bid
   and sell orders at the ask

I'm with him, I'd give all my business to someone who could do that. I could retire in one trading day if I could find someone to do that for me. This was exactly the downfall of Knight Capital Group. It only took about 45 minutes for them to lose $440 million.[1]

Of course, that wasn't what you originally said, which was

   a firm who agrees to buy at the bid
   and sell at the ask

hence the smiley at the end of his comment. There's a difference between "buy at the bid" and "fill my buy orders at the bid". :)

[1] http://en.wikipedia.org/wiki/Knight_Capital_Group#2012_stock...