Well, I agree with you that talking to people online is probably better than not having anyone at all. I myself am not the most extroverted person and have had more online friends than offline. However, I've also come to the conclusion that actually meeting people and doing activities together is so much more fulfilling. You have something you can look back to. Always sitting at your PC talking to people online is surely not as rememberable. What is life when you spend most of the time staring at a screen?
I don't feel it's wrong to have online friends. However, I get the feeling that the Internet makes people become less and less outgoing. Introverts will never learn how to make real friends if they always stay inside. For them, the Internet may work as an excuse "oh well, I could probably make friends in my town, but as I can still talk to people online, why should I bother and get outside?".