I believe there are two factors which separate an above ground from an inground pump.

1. NPSH (net positive suction head) is much lower on an above ground pump since they do not have to prime a pump that is above the pools's water line like many inground pumps.
2. Above ground pumps tend to be lower head pumps since they are usually very close to the pool and do not experience as much head loss as an inground pool.

So the result is that above ground pumps do not need to be as robust and are cheaper than inground pumps.

So while you can use an inground pump for an above ground pool, it is usually overkill.