We don't get a mem usage of 1.7-1.8GB. Our game usually is somewhat between 1GB-1.2GB or 1.2-1.4GB (later on with more characters in the game).
The video is great, but as we use the Unity Engine (C#/mono), we don't do any malloc(). So it's not really our fault, though if we find a repro-case, we'd happily report this to the Unity devs or see if we can find a workaround.
It is a mystery why the OS does not start paging but crashes the software instead if one of those processes gets close to the 2GB mark. Of course, paging won't help if the app needs more than 2GB, but your crashes seem to occur once your user address space exceeds 2GB - which is not the same. All your background apps/services run under your user address space, not just our game.
Definately try the /3GB switch. Though we didn't see our game using more than 1.4GB of RAM. Is there a scenario where the game uses more than 2GB user address space?
We tried to reproduce the error with the process governor but the first part of the game works flawlessly (max Textures, 2xAA, FullHD). When do your crashes occur and what are your settings?