Although, I think there are cases where that would be true, I don't think I agree 100%. I think that there are a lot of people that choose to socialize over the net because it's an easy way to fill (though not completely) the social void in their life. I believe that everyone has a 'hunger' to socialize, so to speak. If the net wasn't around, I believe many of these people would force themselves to go out and make friends so that they could be socially fed.
I've experienced this very personally in my life. There was a time where I was feeling rather lonely and it wasn't until I made the decision to get out there and just talk to people that the loneliness started to fade. I think to myself that if I had chosen to set up a facebook account and make friends that way, that I wouldn't have developed many of the social skills that I have gained from my experiences talking to others.
Of course, I'm no sociologist. Right now, all I have is a bunch of theories about the effect social networking is having on people. Are teenagers that are growing up on the internet going to be missing vital skills that will help them in the work force because they never were forced to just get out there and make friends? I'm not sure and I look forward to the eventual studies that will inevitably come out based on this topic.
P-Worm