Really, the main difference between windows and linux memory usage is that it's hard to get 'individual' or 'correct' on linux.
Thing is, on linux most everything shares libraries - bits of code - between multiple programs. So, if you have three programs all using the same 1mb library, what's using the memory?
On windows, generally programs are self contained packages, and things (seem) to be a bit less cloudy.

Just take it that "linux works this way" and ignore it unless you are doing relative comparisons.