The WSJ had a story on this , and one of the things that they mentioned was that O has accelerated the amount of strikes by predators and reapers.
It depends on the administration, for instance the Navy Seals had a certain set of parameters before they could take out the pirates, and Obama was being kept updated regularly. But a good rule of thumb is that the higher the value of the target, the higher the permision tree.
For taking out that dude, his permission may not have been needed. That the mission crossed into allied territory, or cross border may have required him to green light it.