Curmudgeons of the world unite! I often stay seated and applaud while those around me are standing, but it's darned awkward. You feel like kind of a doofus, and you can't see anyone on the stage anyway...so you might as well get up.
Valerie dates this behavior to the early tip jar years. At the risk of sounding like Joe Soucheray, I'd like to suggest that the "standing obligation" comes out of a "feel-good" culture that doesn't keep score, gives medals to everyone who competes, and wants to be sure nobody feels bad. Of course, then nobody feels really good, either.