I was taking a look at the "Top Game Servers By Players" statistics at gamespy and read this: "35089 servers, 85617 players" for Half Life. Does it mean that there are 35089 servers serving 85617 players in a client-server setup? This comes to about 2.4 players/server. Assuming a server has about 10 players will that be enough to maintain the server? I'm asking this because I have read quite a number of threads talking about how expensive it is to host a server for online games. Thanks.

The cost of a clan running a server (which they rent from an ISP or similar org) is obviously higher than the actual cost to the ISP to run the server. Many of those servers will be empty but companies (ISPs etc) will run them anyway as they have the machine and once you have paid for that the actual cost of running them is low. They are there to attract users who may then opt to rent a server for their clan.

There is also the issue of time of day. Usage of servers varies dramatically depending on the time of day.

Can you please tell me more about what you have just said? I've never heard of "Clans" and this kind of ISP setup. You may also point me to a website with this info.
Thanks.