What a load of rubbish. I have enabled the large addressable memory "mod" and both my 1GB cards are maxed, plus whatever the app is using in system memory. I will look later, but i would wager it is near 3GB total.
He is referring to the main program, not to whatever textures are loaded into your GPU memory. It may be possible that the mod causes the game to shove more textures onto your cards for quicker access, but it doesn't do anything for the main app.
How does your GPU memory load compare with and without the mod? Also, how do you know that you aren't getting redundant textures loaded into your gpus? I'm not doubting that you see what you see, but there are technical consideration as to how the mod works in relation to how the OS deals with memory in addition to the fact that Skyrim's average texture resolution really shouldn't be pushing your GPUs from a memory standpoint unless something wierd is going on. Note I'm talking about vanilla Skyrim (no gameplay/hires mods).
Games like this use texture repetition to keep the memory load way down. I highly doubt you have 2GB of descrete textures loaded in there at one time unless something is astray.
There may definitely be a bug in the memory system that this mod helps avoid though, so you may be right about it working, regardless of how it does it.