I have about 40 tabs opened. One of them is onetab, which has another 18 tabs open.
The reason for that, of course, is that i’m a tab hoarder. But that doesn’t make me less productive. I actually know what’s inside most of these tabs (the icons help). Them being open helps me remember things i need to check or do. Things i can quickly switch to later on instead of googling or going through my bookmarks.
Moreover, when i’m searching the web, I often find something that’s important for my work and keep it open for a while, hoarding a few more tabs in the process. The reason for that is simple — I found that on many occasions i come back to it for more information. Closing it would mean i’d need to scour through my history, or even re-search it — and that’s a waste of time. Every once in a while i clean up some tabs, of course.
So my argument is — the two-tab rule might help for some people, but others might simply work better with the forty-tab rule :-)