I don't know why a Community Manager chose to say such a thing (that Steam charges for the keys)
Look here:
http://www.steampowered.com/steamworks/
"It’s free: There’s no charge for bandwidth, updating, or activation of copies at retail or from third-party digital distributors."
http://steamcommunity.com/greenlight/faq/
"If my game is accepted through Steam Greenlight, can I give my previous customers keys for the Steam version?
Once your game is accepted for distribution on Steam, we will give you as many keys for your game as you want at no cost."
Is that proof enough for you?
And that greenlight faq isn't only applicable to greenlight, you can look here in the web archive:
http://web.archive.org/web/20090226131820/http://www.steampowered.com/steamworks/
Same thing there.
More stuff:
http://www.geekwire.com/2011/experiments-video-game-economics-valves-gabe-newell/
http://www.geekwire.com/2011/valves-newell-predicts-shakeup-for-closed-game-consoles/
Is all that proof enough for you?
See my post above (and many before that)
Valve doesn't charge for Steam keys to devs.