Wikitravel and Wikipedia have incompatible licenses?
I am no expert but I believe the GFDL with clauses as used by Wikipedia and the CC-sharealike-attribution licence used by Wikitravel are only "morally compatible" i.e. they have basically the same intent (viral, free reuse, including making derivatives, is allowed, even commercially, if original is attributed). But they are not legally compatibles for various reasons (I believe).
Thus there has been talk of future versions of each licence being written in such a way to move towards compatibility.