Just thought I'd post a reply to add/update to the discussion, since I just purchased a digital version of the game from steam the other day (previously always used my trusty physical disk).
When I installed the game from steam I was on this weird 1.8 version. I went to search for a server for the first time, there were a bunch of servers named "CoD4 1.7 downgrade", "downgrade v1.7", "MORE SERVERS v1.7" etc. So I just clicked on one and boom fixed. I guess other server owners have cleverly been on the case already!
There were only maybe 3/4 servers for the 1.8 version.
I expect then that most people see the server list and do as I did. Or at least that's what we hope so the player base isn't effected too much!