However, if someone is over-commenting (which is possible in my opinion), chances are that it's because they believe that what they are doing is correct.
I've yet to work with anyone outside of an undergraduate class that over-commented their code.
It takes effort to over-comment code, and those that do are invariably writing both poor code and poor comments.
A much more prevalent malaise is that of developers with an unduly high opinion of their code's readability grossly under-commenting their code. This increases the long-term maintenance overhead and sometimes leads to forced rewrites by follow-up maintainers (which may be the author himself).