"for j as well as p bass...and j and p bass" ??? what are you trying to say there??? i guessing you mean J bass and P bass and also P/J bass..( p basses have only one pup so, no need for a blend pot there) there are many bass guitars that come with pickup selector switches dude, even fender has one...but anyway, here's my humble take on the subject :- since basses mostly use two pups, except for godin or maybe some rare japanese brand AFAIK..using a blend pot will leave more room for tone tweaking IMO.. like guitars, which usually comes with 3 pups or so, basses that comes with two 'bucks tend to have coil selection switches too. they're pretty much the same, you can select which coil of teh two 'bucks you want to use.. Also, JUST A WILD GUESS, using vol-blend-tone instead of vol-vol-tone + pup SS will save the manufacturers lots from a large-scale production point of view P.S - i prefer the blend pots myself
