It's all about distributing the weight evenly, instead of having one or two pressure points. The perfect headband is the one that has the shape of your head, at which point padding wouldn't even matter.
Personally I am more bothered by the vertical compression exerted by the two earpieces. For the weight I always put something between my head and the headband of my phones (because I only have Grados and those headbands hurt like hell after five hours)
Here's a perfect example of me not wearing my Grados (wearing something else!)
(I could wear those like that for as long as I want without feeling it)
Without that cut of a band of foam that came with my window climatizer, the SQUARE headband that is too wide would rest on only one point of my SPHERICAL head, and it hurt me so I DID A MODIFICATION. Hahaha, I have a modded T50RP, it has a foam.
No I mean they really are modified, on the inside too, but you can't see it yet :P.
(too wide for my head, will always end up hurting, I will move it up front or push it further to the back and it'll eventually be unbearable for any section of my head)