So there is a benefit to frequency aside from all other variables (volume/intensity) meaning, take the same volume and spread over 2 days during the week (meaning do not increase the volume - we aren't talking double the load) and you will progress much faster than 1x. Training a muscle 1x per week runs straight into a detraining effect - this is proven. I know this is the way common BBing programs are layed out but believe me they arrived at this through ignorant misapplication because they didn't really understand what was going on and they used overtraining in a single factor theory framework to make these changes which was very logical except that single factor/supercompensation isn't right and when this change was going on in BBing the whole world already knew it wasn't right but nobody bothered to ask or look. The whole world designs programs much differently under dual factor theory. When I say whole world, I mean among every serious strength coach (this job includes adding LBM to athletes in a time constrained environment) and researcher around the globe at the highest levels there is virtually universal consensus.
Anyway, here is a post I wrote on the subject specifically explaining how BBers arrived at the 1x per week method. Post #234 on this page
http://www.elitefitness.com/forum/showthread.php?t=375215&page=12&pp=20
You might also check out the post immediately below it. There is a link to an entertaining interview with Glenn Pendlay who I happen to think pretty darn sharp when it comes to this stuff. His lifters routinely squat 3x per week and pull 5 days, make huge gains and do it all clean.
This thread has a lot in it but the first page is primarily an illustration of a program based on dual factor theory. It was designed by one of the best strength coaches ever - Bill Starr, and has been used in one form or another for over 30 years. There is really not much out there that can compare in inducing hypertrophy.
http://www.elitefitness.com/forum/showthread.php?t=375215