I have to thank you, other players on my realm. If it wasn't for you, I probably wouldn't have reached 450 Skinning already. Yes, the garbage of dead mobs that you leave behind becomes my profit -- when you leave that worg corpse or the dead drakonid behind, I'm all too happy to run over, skin it, and clean up that little mess you've made, while sticking a little gold in my pocket as well. Matthew is right there with me -- he calls it poaching, though we're both referring not to stealing, but to simply skinning the leftover mobs of all those players before us.
Truth be told, I probably poached more than ever down in the mines of Netherwing Ledge -- there were always players killing down there, and what they didn't skin, I did, both for the quest skins and for my own Knothide. But in the expansion, things are even better -- everywhere I go, there are fields of leftover mobs, and even when someone is able to kill a mob before I get there, I hover over them to pick up the skin afterwards.
Matthew has put together a list of all the great places to pick up extra skins -- I'll agree that Coldarra is full of poaching options right now, as is Kamagua on the other side of the continent. Grizzly Hills, also, is not only full of creatures to skin, but lots of leftover corpses as people quest across the zone (though odds are that if you keep up on skinning, you'll be 450 by then anyway). Think of it as a service -- we're the garbagemen of the realms, cleaning up your kills so the next can spawn and the circle of loot can go on.