Exactly.
Even the best virus scanner is only an addendum to the core rules of virus protection:
* Never download something [web or email] unless you know what it is, and whom it's from.
* Scan files before you run them.
I will agree, you must update your virus scanner, be it AVG, Norton, anything else. I update mine at least once every couple days. And none is perfect, you shouldn't rely on just one.
That said, in about 7 years of hardcore computing, the only virus I've gotten has been from a friend of mine sending me an email saying 'is this a virus?' [it was.] And I've been using AVG most of that time.