Your trying to compare apples with oranges, Tennis are only looking at line calls. Cricket also has issues with catches that touched the turf being inconclusive and as I already stated close runouts that are occasionally inconclusive.The speed of the ball as cricket level is triple that of AFL, same with tennis. If they can get the camera's right the AFL has no excuse.
The fact is TV runs at 50fps and everything moves that quick that your left with blurred footage when zoomed in. Anytime you try to enhance the footage after the fact you will have issues with fast motion. A fixed camera in a spot zoomed in is ideal for the goal line but that doesn't help when the ball is away from that area.