It isn't really much trouble to click twice on the back button to go back one page but the reason should be a security concern. It appears that google and doubleclick can guide a visitor without detection on this forum. The Baynet is worse (not your concern but it shows how this can escalate). On Baynet, the first click brings up new ads. I don't see this on any other sites I visit.
http://forums.somd.com/about-somd-com/234674-google-doubleclick.html