No.
The problem is that CSSports don’t “see” a lot of BF2 servers. Gamespy, on the other hand, hosts BF2’s master servers - so they have the most accurate server count for BF2. It’s like going to steampowered for HL1/2 stats or Microsoft/Bungie for Halo stats… they’ll always be more accurate.
Both have more-or-less the same number for ET players (~9,000 right now on CSSports, ~11,000 on Gamespy - more!) but very different for BF2 (Gamespy lists ~30,000 BF2 players right now, CSSports has ~9,000 right below ET). It doesn’t take a genius to see the problem is that cssports is ignoring a lot of players/servers (and no, BF2 doesn’t have online bots).
And not really ‘a lot of people’ quit Bf2. http://www.flickr.com/photo_zoom.gne?id=125077149&size=o shows it has been quite stable on the past few months although it’s dropping very very slowly.
Now, does this mean something?
No, unless you like to look at things with an e-dick mindset. More or less players doesn’t mean a game is better or worse. Guess what, you have choice.