As someone pursuing a PhD, I can tell that you that if you say "I'm doing a PhD in computer science" or "I'm doing a PhD in human geography," you still get the follow-up question, "so what exactly are you studying?" It's natural for people to want to engage you in conversation about your career, even if you both know that the minute nitty-gritty details are going to be far more involved than anyone would really want to hear about at a social gathering. I give my "elevator pitch" about my research, just like any founder would about his startup. If they are genuinely interested, then I talk about it, if not, I move on without getting hung up worrying about it. I also think that in this area at least, the "founder" vs. "normal" distinction is a bit unhelpful; many of the points you raise can be applied to most occupations.
