Precisely. Valve builds stuff largely to drive some kind of idea forward so hopefully other devs will copy it and people will buy more games. They also want them to make money, but they make so much more through Steam than any of their games that it's not really worth the investment. Counterstrike (their biggest cash cow) makes ~$1B, Steam makes ~$10B (estimates of course). Most of their games are way below either numbers in total revenue ever.