Why is that surprising? They have exactly the same meaning; the difference is that 'but' additionally carries information about the subjective point of view of the speaker. (Where 'and' indicates that two things are true, 'but' indicates that (1) two things are true; and (2) the speaker considers this surprising or anticipates that the listener might find it surprising.)
coordinating conjunctions are wierd. and, or, for, but, yet, so, nor. Nor is sort of an oddball there, since it continues negated clauses, well I use it to. - my jeans were neither creased nor dirty. Yet fits in a ton of places as well.