Well, am not the oldest guy around here, probably. But I think there is a growing tendency now for men/woman to spend their time/money on things other than "Socializing". Quite many of my friends spend their money collecting figurines or video games or whatever, and though they are interested and in need of meeting strangers and the other sex, they prefer to keep such interactions to a minimum and find the whole "mating ritual" too complicated. (I admit that my circle of friends is composed of rather like-minded individuals). Hell, there is an entire
movement for this, provided it deals more with the rejection of society's expectations.
So yeah, I guess it's impossible for the people aforementioned to live as shut-ins because there is no financial support from their parents for this kind of lifestyle. But they simply evolved now and kept their social interactions (and interests) to the bare minimum.
I imagine that if they had rich parents who allowed them to do anything, they would live as hikikomoris, but if those japanese shut-ins were forced to go out and work, they would still simply work and socialize to feed their own isolation, in their own little way.
I actually tried understanding why they do what they do, and I was met with an interesting answer, "Why not?".