Sure, some HN users are going to be McMaster Carr users. Some HN users are probably Boeing customers as well, but I wouldn’t trust HN’s collective assessment of the procurement UX for a 787. The users who McMaster Carr is targeting peripherally intersect with the HN community. And it also happens to be a community that contains people who are more likely than the average population to enjoy browsing a parts catalog for fun.

I just don’t know how much you can conclude generally about effective e-commerce design from that sample point.