Invisible Walls

[Feyniphia]

Being able to step on the cliff or not has little to do with hardware limitations (unless they didn't make/wanted extra collision data). Also Skyrim isn't exactly zoned.
Aion, for example, is a zoned MMORPG, yet you can climb pretty much any mountain. Yes, you do sometimes see the "end of the world" and the void behind, but that's another point.
You can place high enough mountain to stop people from going/looking over. In this game though we got walls in places that aren't even close to the end of the map.

Oh well, wait until they make useful stuff there, but for now, endure it. :P