Anyone noticed this about WB?

I put a Widgetbucks widget back on my site and beyond the fact that the holidays seem to be playing havoc on their statistics, I am wondering about something.

I only seem to get about a third of the impressions that Analytics tells me, even though the widget is embedded in such a way that it is displayed on every page.

Is this normal for you all too? While I understand that only the US and Canada traffic is counted in the non-international impressions, there is still a wide margin between what Analytics says and what WB says. What other factors are there?