In the case of "demonstrated" it is a hint, in case of "max certified" it is a setting for allowed POH operational limits. In first case and an incident you underestimated your skills, a mistake, in second case you violated operational limits. And be asured, a 1955 C172 will be case 1, while an after1986 C172 may be case 2.
This statement (and kind of thinking) muddies the waters needlessly, and is not a good basis for pilot decision making. The phraseology of flight manuals was standardized in the mid '70's, and "demonstrated crosswind" was on of the elements captured in that. As can be plainly seen from the POH wording presented by Chicken House, the referenced POH specifically states that the crosswind value is "rather than airplane limitations." not limiting - it's not stated in the limitations section as a limitation. It's a value demonstrating the aircraft's capability.
I cannot speak as an insurer, but I would not accept denial of a claim for a crash when no limitation was exceeded, and the aircraft was being flown with good airmanship. I agree, that there comes a point where an attempt at a crosswind is too much, and that would be poor airmanship in attempting it. I think insurers sometime even pay out for poor airmanship, but I've never tried....