^ most companies will advertise the nut busting because the numbers are higher so it looks better. It has to do with the fact that it is easier to loosen a nut than to tighten it, at the same "position". Friction, thread shape and all that. But from what I remember reading, it seems like the difference is only of the order of 20% or 30% or so, not sure though.
Having said that, the concept does make sense because you want to know if you can remove with that power tool a nut that was tightened to a specific value. Whereas it is usually not a good idea to tighten a nut with a power tool if you want to be safe (yes, there are torque bars and all, I know).
FWIW, the "Torque Test Channel" on YT has tons of info on all sorts of impact wrench models, reviewing and testing them all, ranking them etc. Very interesting.