Abathur can gain xp in a lane without being there with his symbiote, or if he has a live locust in the lane. What other heroes have a mechanic like this? Do Azmodan's spawns earn xp in a lane without Azmodan himself being there? What about Gazlowe's turrets, Malfurions Treeant, etc.?
While any hero that summons other entities to do damage can get experience from a lane without being in the lane, Abathur is the only reliable one. Summoned creatures (Malfurion's treeant, Zagara's zerg summons, etc) or weapons (such as Gazlowe's turrets or Sgt. Hammer's spider mines) only give you experience if they get the last hit on a wave minion. If they do not get the last hit then you do not get experience, even if they are near the wave or have done damage to it.
Abathur is special in that when he places his symbiote on an ally, whether that is a wave minion, a camp minion, or his own locusts, the symbiote counts as him being there and will soak experience. His locusts act like any other hero's summon and do not give experience for just being nearby, only if they get the last hit.