I agreed with your first post. I am also holding out for the thought that there are exceptions. Interestingly, this comment stood out to me: "That is mostly because eBay is a generally badly designed site. They have one of the most averse-to-change user bases on top of it, so bad decisions stick for a longtime." But they have a huge userbase. Transactions are happening. This is where my confusion kicks in... People claim a site has bad design, but a ton of users actively use the service. I would venture to guess that a large percentage of those users are not tech-savvy.

So what is the measure by which we are able to claim that some site's design is "bad"? I provide the counter: large, active userbase and a lot of money moving through ebay. Perhaps not enough money goes there? Do we think someone could create a competitor to ebay with a "better" site design and steal ebay's crowd? What role does site design actually play here?