Tony - you mean the part where you bend over and target is down low?
I wouldn't call that a bob really, more like dealing with a low attack or low shoot, although I favor a low compression of the stance and bui jee hacking elbows..
Many southern styles don't really bob and weave in the conventional sense because it whacks your structure.. The bob and weave is great in boxing because of the limited number of attacks allowed to the upper body. When you add in body checks with structure, energy/balance attacks, leg attacks, knees, elbows etc, leaning outside your center of gravity <moving the head mainly> can put you into an unrecoverable position that may result in a loss of balance, falling or inability to attack, something, in general, boxing does not emphasize or worry much about.
Body movement that uses similar lines of evasion and attack should be present but instead of the bob and weave the whole body moves just a little offline and in, a la Sanchin, but with the counter, just as in boxing you can slip inside the attack with your own but one is done with a leaning over while the other is done with the spine more or less straight to maintain the kind of structure these styles use to generate body power, maintain balance and protect vital areas - in theory...
THAT'S NOT UECHI!!!!