Also, part of the problem is there isn’t really any incentive to say “We use CI”. What’s the upside? If you are a big name, being listed as a CI project doesn’t mean much to you. If you want to get listed, its probably because you don’t already have a lot of mind share or traffic.
Facebook, as far as I’m aware, is a bit unusual in that its actually clear its written in PHP. Many big sites don’t even expose that much information about their internal system. Twitter is unusual in that it actually says its built on Ruby On Rails. Google uses a big hodgepodge of languages including C and Python, but doesn’t admit to using much of anything that they didn’t themselves create.
It’s not that I don’t agree it would be nice to list some more big projects, but I guess I’m at a loss for what the actionable step really is. If they already know it uses CI, it’s probably on the list. But if they don’t know, how can they find out? There is nothing in the system or structure of CI that gives much of any hint that CI is being used, save perhaps the 404 error page - but any big project would over-ride the default to provide their own implementation of that, anyway.