Just to clarify my position on this...
Personally I do 1 or 2 sets of bicep work a week, same for triceps, after having been on rippetoes routine for quite a long time now.
I don't think an 'arm day' is necessary, but I do believe a little extra focus on the arms in the form of iso exercises is beneficial to those seeking to improve a lagging body part.
As for the sheep mentality, its definitely here.
Cobra, Curry and the Gibson Flying V.