Well, Ron Carmel, World of Goo dev, tuned in at the GDC about Steam saying that it took them about a week to get the paper work done to get their game listed and sold on Steam, where it took them 4 months to accomplish the same thing for LIVE. They also said Steam throws a lifeline to indie developers because of how they increase awareness of indie games to such a big audience of gamers so fast and because of the significantly smaller profit margins Steam makes, passing on much more money to the developers than normal publisher/distribution agreements (which force even big dev studios to "survive" project to project).
Tripwire Interactive also said in response to Gearboxes' Steam bashing last year that, "Without pulling any punches, I can say with certainty that if it weren't for Steam, there would be no Tripwire Interactive right now". "Ask Garry Newman, creator of Garry's Mod, or Dylan Fitterer, creator of Audiosurf if they feel exploited. Ask the Tripwire Interactive employees if they feel exploited, as they move into their new offices paid for by the money the company has made on Steam," Gibson asserted. "Or me, as I drive away from the company that was built from the royalties we made on Steam, in my sports car paid for by the royalties we make on Steam, to the home that I pay for with the royalties we make on Steam."