This is also my experience when running other games like Enemy Territory for instance. I know the game itself isn't as fat on Linux as it is on Windows. I don't remember any numbers for the game itself but I can give you numbers on the dedicated Enemy Territory server. When running A dedicated ET server on Windows it will gobble up a bit over 200 megabytes of memory. When doing the same thing on Linux, the process will gobble up a bit under 100 megabytes.Interestingly, the system requirements for the Linux version are lower than the Windows version. Whereas Windows requires a 1.5GHz Pentium 4 and 384MB of RAM, the Linux version, according to id, will quite happily trundle along on a 1GHz Pentium 3 and 256MB of RAM.
Lets face it. Windows is bloatware and so are the apps that run on it

Btw, my BP6 gets ET server duty once a week and it works just fine for that purpose.