I would agree that the extent of rimming we see these days was simply not there 10-15-20 years ago. This applies to both the real and the porno worlds. Rimming is certainly no novelty but the extent of it somewhat is...
I agree with SC that the condom issue has a relevance here and that the producers who want to sell, feel compelled to show as much flesh as possible.
I have little doubt that porn played a major role in making it a 'standard repertoire' for most players as well.
Another major 'novelty' is that being homosexual has become far more acceptable to both the gay guys and the society in general. I tend to believe that this climate helped many gay guys overcome their inhibitions. I still vivdly remember my college days and the rumours about few guys 'who were willing to work their tongues up your ass'... For quite a few gay guys this was some sort of an ultimate taboo. They were fooling around with other dudes. They were all doing the usual stuff but rimming was just not there. To most this was just gross. To the others this was an ultimate humiliation and an act of total submission. Getting fucked was sex. That was fun and OK to most. Kissing other dude's ass was viewed as some sort of a pervy submission frequently associated with guys who were not doing too well on the daily cruising market and were thus willing to go to any length to secure some daily cock. All this has radically changed.
IMHE, relatively few bttm dudes really expect to be rimmed by their tops. Sure, if the top goes that way, hardly anyone would say 'No' but most bttm guys seem to be happy with some lube and the action which follows...
Just my 2 cents...
KD