To me they look almost identical in material, thickness... but the diameter of the opening for the ATH's is probably a couple mm wider. They're more comfy as they side more 'around' your ear, but I feel that also reduces the seal a bit. So this effect is probably somewhat dependent on user.
I took them to a noisy coffee shop and they hardly isolated at all. But they do sound pretty great with my Nexus so at least they have a home for that use case which is probably how I spend a good 10-20 hours per week.
I am in concurrence, it seems the diameter of the opening has great influences on the bass.
Which is probably why JVC choose to stick those pads on there, it seems a smaller opening would increase the bass boost but muddy up the mids and a bigger opening would bring the mids forward but at the expense of a weaker bass.
Real pity they did not try making them original pads more comfortable, otherwise we wouldn't have to wade thru the swamp of alternate pads !