Why do people that aren't around seem more real than those that are? I've pondered this a lot.
I think there are several blending aspects; we'll see what I can mold into words onto ... paper? whatever this is. :)
For one thing, the people around us become a blur -- they're there, constant. You only begin to notice the things that surprise you, and those begin to surprise you less and less. Unless an active effort is made by them or you, the world greys.
Online, life that exists is by definition to some extent active. If the person is not around, they don't exist. If the person says hello -- online -- that's an active thing, above and beyond what you expect from noncorporeal entities.
Of course, there's also mystery, the attraction of new things, generally only the positive things about a person really get projected over the copper and plastic lines that weave this network of souls. La la la.
That's at least some of it.