Does a level 30 player, for instance, have the ability to get closer to a level 10 mob than a level 10 player before it will attack them?
Yes, the higher your level compared to theirs the closer you can get without drawing aggro.
I see this whenever a much higher friend helps me out, and effortlessly runs through a scattered group that I cannot run through without drawing aggro.
Also, some mobs have larger aggro radiuses than others. I suppose the mob type is supposed to have higher sense abilities when that is the case.