You're absolutely right, Lorna. I also struggle to understand why one wouldn't want to go out and engage with the community, give up weekends to attend BarCamps or user-group organised conferences, or nag the boss to let you go to every event that the budget will allow.
I do know that I wouldn't be where I am today in my career if I'd just worked 9-5. Friends might take the piss out of me for going to "GeekCamps" as they call it (I try to explain the free food and drinks but they don't understand!) but I would not - and cannot - give it up.