Isn't the API just storing in RAM and letting a page file do its thing?
In a 64-bit only world, that isn’t a bad strategy. I would guess a lot of this is just legacy from having to or having had to support 32 bit OSes.
How do you make sure that the video doesn't push something far more important to the pagefile? Does windows have a way of telling it the priority of an item in memory, or do you have to trust a caching algorithm?