I agree with Colin in part here:
Two different organizations but with two different objectives.
AQ wants to cause uprisings in Arab (they say muslim, but it's really Arab) countries to trow out the various dictators or "entrenched" families and then, turn those countries into "proper" Islamic republic (A la Iran, but in each country - see recent Bin Laden's son statements calling for uprising in Saudi Arabia). So they don't need territory to exist, only to cause existing countries to become Islamic republics, then they dissolve or disappear. Their terrorism in the West is aimed at causing responses by the West but in the middle east, so as to cause the said uprisings.
ISIL wants to be a Caliphate, that is the unified Islamic "Umma", thus wants to govern and needs, by definition, a territory to so rule based on their interpretation and application of Islam - said territory to be expanded until it covers all the earth and all are "good" (according to them) Muslims. Territory is essential to their existence and it is doubtful that, fully deprived of any territory, they would continue to exist as an organization - though it is some times difficult to see if their various forays into terrorism in the West is aimed at the establishment of the Caliphate in the West or simply at causing reaction in the West that drives even more innocent people to join their side at the current location of their "Caliphate".