The only observation I have, is that the true "expert" users are developers, who may think they are users, but they really aren't. For example, it is very rare for me to work on a project that has me as an intended user. Usually I'm developing software for people whose work is nothing like mine, people who really don't care about computers other than as tools to get their work done.
I cover this in more detail here
I am definitely an "expert" user of software, so I see things differently than these users do. I think these are the kinds of expert users Cooper was thinking of-- inappropriate users. Real users would never achieve this level of expertise with software, because they have other things to do!