From a training and proficiency standpoint, it makes sense. If every one could fly all flavors of 767 and 757, aren't there 6 or 7 different fleets?

That's WAY too much Differences Training for me to keep track of. It makes me wonder if the POI thought the same thing, from a safety standpoint.

As an example (as I understand it), SWA flies 300s through 900s because all of their airplanes are more or less configured "300-esque."