Double vs. single saddle rails? Looking into buying myself a Brooks saddle, and have found two models that primarily differ in having what the descriptions call "single" or "double" rails.

What in the world is the difference, and why would I care? (Rhetorically: why aren't there pictures of the undersides of saddles so that I could work this out for myself?)
A modern saddle has a single rail on each side that starts at the nose and runs to the rear of the saddle. A single or double bolt clamp attach the saddle to the seatpost. The Brooks web site show some profile images of their saddles. The images show two  rails on each side of the saddle. They merge together at the nose of the saddle. They are reputed to be the most comfortable of the Brooks line. Be aware that the images show a double clamp to attach the saddle to the seatpost. This will require an old style seat clamp (Brooks part# BYB 105) and seatpost.