Whopity, my understanding is that the demonstrated crosswind means that during the certification process a test pilot landed the aircraft successfully at that windspeed as confirmed by ground instrumentation. There is a minimum crosswind of 0.2 Vs0 that must be demonstrated for certification purposes, but there is no maximum limit on the crosswind component that may be demonstrated.
As Taybird pointed out, the limit may be real - in that nobody could land at a greater crosswind without breaking the aircraft - or it may be that the aircraft can land in much stronger crosswinds, but nobody has demonstrated this officially.
I guess this latter case surprises me because I would have thought that crosswind capability would be an important factor for anybody trying to buy an aircraft and it surprised me that manufacturers might not try to obtain the best figure possible. Secondly whilst I recognise that it is not a 'limit' in the same way as Vne, I don't recall reading any guidance regarding structural versus aerodynamic versus sane crosswind limits for the aircraft I have flown and in the absence of this information how is a pilot to know whether landing slightly above the demonstrated limit is in fact sensible?
Now, my understanding is that certification isn't easy or cheap and can't be done in a day, so when I see a C152 with a demonstrated crosswind capability of 12 knots, it strikes me that the test pilots must have had the opportunity weatherwise to obtain better figures, and it still baffles me that they didn't.
If you can't be civil, at least be constructive and point out to me where my misunderstanding lies.