I recall A-10s sometimes carry two Mavericks, one armed and one disarmed to use as a target designator. That might be it but since the Hellfire has a purely passive seeker probably not.
The other possibility is that the Predator is carrying a Finder mini-UAV in the other pylon to locate targets.
http://en.wikipedia.org/wiki/Miniatu...d_.22Finder.22
It's also not unknown for Predators to carry just one Hellfire in combat. Maybe they don't want the operators wasting $60000 missiles.
The reasons why are probably classified, but I don't know if it's normal to fire two Hellfires in flight because the airframe can barely handle one launch without falling apart. The Predator actually uses a special Hellfire with reduced thrust to prevent that.
But since I see pictures of MQ 1s with two missiles all the time, it probably makes sense to change the Predator loadout to two Hellfires.