The matchmaking system that's been forced upon us has worked surprisingly well to be honest. It saves messing around trying to find a good server, although lag is an issue because of hosts with terrible connections I probably only experience this maybe once every 20 games. This system certainly has it's advantages for our crowd as you've mentioned
but overall I think I've been fairly satisfied how it's worked out, although I think a large majority of the MW2 community isn't prepared to admit that.
As for MW2 outselling COD4, that's no surprise this game has been greatly anticipated since it was announced and has earned IW a hefty bag of cash.