Why do video games use so little memory?

So I have just installed Warhammer DoW 2 Retribution. My PC is almost 5 years old and even though it doesn't meet even the minimum requirements, I can still play that game on lowest graphics with almost no lag. I opened Windows task manager and noticed that the game uses only 200k-300k memory and with everything else summed up it reaches 450k memory. Shouldn't Warhammer use more memory? And it's not the first game that uses only 200k-300k memory. I remember checking CoD Modern warfare on my PC and my brothers new laptop, I used the same settings, but CoD on his laptop used over 500k memory. I have 1gb ram on my PC, I use windows 7. The task manager shows that I'm using only 44% memory while playing games.