"because it seems like it would be so easy for the band to do this"

Dude, don't say that, unless you really think anything that they do is "easy". Its just poor form. I say this with total respect for your comment and the one's you've made previously, and I agree with most of what you said, but let me propose a reason for the multitude of short songs in their sets.

They just don't tour like they used to... they spoiled us back in 97 when they could play pretty much their entire catalog and also extend pretty much any song for as long as their curiosity (and chops) allowed it to. That was a perfect combo of over a decade of dedication to their craft and a new-found interest in (and ability to play) funk, trance, and other infuences. With an abbreviated tour schedule (these guys do have families), they are trying to balance actual live experience with their catalog (which is vast) with improvisation. Their simply aren't enough tour-hours available anymore for them to play a 50 min Jim, except for every once in a while... maybe... hopefully