"...when exactly does any computer bought at the same time (or since) have actual problems of running out of memory?"
Ah yes, I remember the days being a dev that didn't use VMs. It kinda sucked as a development environment that said: no easy way to test software on different OSes locally, no easy way to try other software which you don't necessarily trust in a confined environment (to see if it may be worth using, in which case you'd look into the trust issue more closely), etc.
If you're a dev and have "enough RAM" you're probably not trying hard enough ; )
VMs tend to use quite a lot of memory and tend to be very useful for knowledgable devs.
You asked and seemed so cocksure so these were my 2 cents...