That's exactly it, isn't it? These PageSpeed "warnings" are just the same - to the peeps who are not interested in the W3C "standards" warnings but do apparently pay attention to SE tools warnings :o please do listen to sage advice like Swa's
perhaps that's about the best explanation I can give too :) except replace "W3C CSS Validator" with the words "Page Speed"
we agreed that a long time ago JAB, it's just that we might have a new phase/different "validator" going on here, so which would you use - the descendant/child selectors or the extra classes..
and just to remind people (with Tin Hat on) do you think the SE's would be able to parse/understand the stylesheet better with or without specificity and inheritance?