Steam is a digital retailer, they do not provide servers. The developer of the game sometimes provides servers especially early on so gamers have somewhere to go. But usually gaming communities, clans & even outside companies like video card vendors provide majority of the servers.
In regards to Call of Duty Black Ops it will have dedicated servers on launch and I have no doubt there will be plenty online when the game launches either from the community or Activision itself. Just note that in Black Ops all servers are run from the same company due to an exclusive deal Activision has with them.
And yes there are about 2500+ servers in Battlefield Bad Company 2, with thousands if not more playing at any given time. Since you're new to it I'd recommend going to a server that is more beginner friendly, they tend to be named something like "level 25 or less only" etc.
