Rivendells are highly-evolved versions of the Bridgestone bikes that Grant Petersen designed. There were quite a few things Petersen wanted to do with the Bridgestones that were vetoed by head office in Japan (longer chainstays on the RB-1, for one thing). And Petersen's design ideas have changed substantially since Bridgestone USA shut down. A couple of examples:

-Compared to an RB-1, the Rambouillet (which used to be known as the LongLow) has longer chainstays, lower BB, slacker seat angles, higher head tube, shorter top tube, and greater tire clearances. That's not even considering the beautiful lugs, fork crown and numerous other examples of quality detail work on the bike.

-You could also look at the Atlantis as the descendant of the Bridgestone XO bikes, but the bikes are so different that it would take too long to list all the changes. The Atlantis is, IMO, a far superior all-round bike to the XOs, which had too-short chainstays and too-steep head angles.

-Of course, there are no Bridgestone equivalents to the Saluki and the Glorius/Wilbury, and the custom Rivendells are tailored to your riding style, as long as that fits within the Rivendell design philosophy.

I've owned 3 Bridgestones ('92 RB-1, '92 MB-3, and '93 XO-3), and they're fine, well-designed production bikes, but the construction quality is merely good, not great. Plus, I've broken two XO-3 frames in the same spot each time (base of the seat tube socket in the BB shell). Rivendells and Bridgestones were designed by the same guy, but don't make the mistake of thinking that Rivendells are merely Bridgestones with nicer lugs. There are loads of differences.