Well, perhaps, but really it is one of the apps that, when it came out, helped define the term. So one would have to call it retrospectively silly. In my mind any terms can be silly depending on how you look at things. But it seems to me no more silly to call digg web 2.0 than gmail. I will agree that most of the apps that have been called web 2.0 have been social, but most of the apps of any kind have been social, which is, as I see it, part of the problem. social != $$$$.
I'm going to say something unpopular and lose friends:
Who the hell CARES about the term?
Gmail is a good application. Digg was a good idea but it didn't scale. You can argue about Web 2.0 all you want, nobody cares. And you can go out and make money right now, and that's a fact regardless of whether you're 2.0 or 3.0 or whatever in between.
I never got the reason behind the "2.0" buzz. I never will. It's such a pathetic waste of time.
The exception to 'social != $$$$' is of course Google's page rank algorithm which is essentially a social/collective intelligence system. The financial success of first Google then other companies is probably what motivate the term more than anything else. It is a shorthand way of saying
'The internet is not a financial failure. It's back and we it doesn't need all those MBA's who helped create the crash in the first place.'