They have always warned prior to attacks just not in such a brazen way in the past. They have been warning and/or going through all the Islamic laws in preperation for the next one quite strongly for the last year or so, and probably back to 9/11 to some degree.
the problem is what is propaganda and what is actual warnings. the problem i have with recent people talking about attacks is that they seem to be obscure people and not the talking heads of bin laden, al zawhari or the traitor