Gameserver with a large number of slots have always been very popular for regular public gameplay. Games like Battlefield 2 changed online gameplay as they allowed up to 64 players on the same gameserver. Counter Strike Source even supports 64 players, although it’s a laggy experience for most players. Big servers are more expensive, but have always been the people’s choice.

New games like Team Fortress 2 and Quake Wars have been optimized for 24 players. They both limit the maximum number of players on this number, TF2 uses serverbrowser censorship, Quake Wars has been limited in the ranked server software (unranked supports up to 32 slots). Other upcoming games have also a lower limited number of maximum players. The Unreal 3 engineused in Unreal Tournament 3, Medal of Honor: Airborne and Frontlines: Fuel of war does support 64 players but not one of the three mentioned games uses servers larger than 32 slots.

Client-server model supporting up to 64 players as provided. Also supports non-dedicated server (peer-to-peer mode) with up to 16 players.  

This specific engine does support a second networking model: a peer to peer gameserver network model that supports up to 16 players. This is primarily used on the Playstation 3 and XBOX360 version of games using this engine (ex: Gears of War).

The lack of game supporting large gameservers will be the reason Battlefield 2 will be one of the most played online FPS in the next year, at least until Battlefield 3 is released.