Maximum demonstrated does mean just that - it's the greatest crosswind seen during certification and found acceptable.
The CFI at my club is ex-airlines, and he told me that one of the aeroplanes that he flew had different max demo'd limits for crosswinds from the left and right due to the weather during certification.
I believe that it is possible to get the max demo'd crosswind increased. I know of one company that was trying to do it, and last I heard it seemed likely to succeed. The original limits were rather low though.