Not sure if I understand the second part.
Valve, being the developer of Steam does provide some dedicated servers for the own games, but it's not they're responsibility to provide servers for all games on Steam. That's up to the developer and publisher of the game, not Valve. Most games rely on dedicated servers hosted by gamers and developers alike.
There is some Steam integration that the developers can take advantage of if they choose to; such as Friends, Workshop, and Matchmaking. Since a lot of games use dedicated servers, matchmaking isn't used that often. Now-a-days most multiplayer games do take advantage of Steam Friends, so you shouldn't have a hard time finding your buddies.