I agree about the overcount vs undercount thing, but I think Clicky's method is much closer to the "truth" of site engagement. Tabs aren't used much outside of the "power user" world. Typically when people go to a page, it is the page they are reading.

We do want to make it smarter and only ping when the tab is in the foreground, as that will make it more accurate. It's a planned update for the future.