"It turns out that the vast majority of all IE sessions contain three or fewer tabs. Accordingly, in Beta 2 we try to give users three efficient tab processes. This is contingent on the user’s computer capabilities, but the more capable a computer is, the more processes we will use, up to a point. Adding more processes gives users much better isolation in the event of a failure. If each tab is in its own process, websites are completely isolated from each other."
Source: http://blogs.msdn.com/ie/archive/2008/07/28/ie8-and-reliabil...
That's only because tab management sucks when you put the tabs along the top of the screen, and the lack of organization means people feel obligated to close things out or re-use them rather than popping new tabs.
Since I started using Tree Style Tabs in FF, I'm averaging somewhere around 50 tabs up at a time (of course, I don't even notice this until FF tells me the number as I close out, since they're all collapsed and well organized).
Also, IE8 creates separate processes for each tab, just like Chrome. Obviously Microsoft can set whatever double standards they like, but excluding other browsers would pretty much guarantee the Justice Department re-entering the mix.