I generally consider the total weight of my bar and plates. I think Cathe uses the York barbell, which is 5 lbs (or less). But if I'm using my 15-lb bar, I want to count that weight toward the total.
I think you have to pick a standard and stick with it -- for example, always include your bar or always exclude it. That way you can judge your progress (especially when doing STS).
Having said all that, I believe that Cathe includes the weight of the bar because it looks like she has on two 10s, two 5s, and two 2.5 lb plates when she says 40 lbs. That, plus the bar, would be 40.