I think you're misunderstanding me.
yeah, that demo looked amazing. And it used less than 4 GB of available RAM. The point is that late next gen, we should expect stuff to look like that and take place on much larger scale. That level of fidelity in a bigger space with more characters and more interactive items requires more memory.
my point was that we can't sit back and say that 4.5 GB will be plenty because of the tech demos we saw. More memory is always better.
And, honestly, it still makes zero sense to me for Sony to double the RAM, eat that extra BOM cost, and only give developers an extra GB o so to work with. Especially since they said publicly that devs were asking for 8 GB - assuming that most of it would be usable to them.
This whole thing is just super weird. Either Sony wants to shoehorn multiple running apps into the PS4, or the OS as they've shown it so far is just a RAM hog