Wow these guys for this months symposium award please.
Also, it's not really socialising to the same extent as actually being out, face-to-face. "Social skills" has always meant your ability to intereact with other human beings, not words on a screen. The nature of the internet is such that you don't have to be a real person, you can plan out everything you say and take as long as you wish to react to something that's been said to you. Whilst you are still "socialising" to a degree, it's a completley different skill-set to that used in every day encounters, and it's the deficit of those skills that parents worry about. In honesty society is very close to the point where, from a certain age, someone can very well get along without ever leaving their house. However even people who spend the majority of their time on the PC wouldn't choose that life, but may find themselves edging closer to it. Some people aren't like this and are just naturally able to socialise regardless of how they spend their time. Others who are more prone to shyness, anxiety or people who have bad habits (read: people who are dickheads) need to actually socialise regularly so they don't "forget" how to.
The above contains 10% argument, 90% hypocrisy.