I still think that "warmth" is a way to describe not actually hearing the separate digital samples subconsciously, and just hearing the sounds gliss into each other. I also think it's an anachronism that comes from way back when the digital sample rate was often a lot lower (and people would insist that their live digital effects sounded as good as analog, when you could sometimes even consciously hear the samples jumping into each other.) Other than that, it seems like something that people project onto music with bassy reverb.