I would suspect the "new" axles will have a more effective anti-corrosion coating.
I have been keeping an eye on my rear axle and the front sub-frame, looking to see if there is any evidence of corrosion. So far, so good. My van gets little salt exposure, so even though the ac unit runs nearly year-round (dripping down condensate at the rear and the front) there is no paint wear-through ... yet. I keep planning to put more insulation on those ac lines in the left-rear wheel well ... but still haven't done it.
I long ago bought a new sub-frame as the original had some pretty severe road-debris impacts. So far, (422k miles) I haven't replaced it. I will paint on extra protection before replacing ... if ever.