I still manage to put a couple thousand miles a year on 2004 a carbon/steel LeMond and can say I have no concerns with the joints whatsoever and its one of the best riding road bikes I've ever ridden. That said, it would likely still be that way if it were all steel, or all Ti for that matter. I would tend to agree that marketing or the "our bikes have carbon too" syndrome led to the proliferation of bikes with at least carbon seat stays. Next frame will likely but all Ti custom.