There's no such thing as a stupid question..oh yeah?

That was Sarasota twenty years ago, Palmer. You should see this place now. It's doubling again!

But back to the issue, the end nut, washer and cotter pin assembly essentially hold the wheel on, yes. The nut is tightened to allow the hub to spin freely and the cotter pin holds the nut in that position. As wheel bearings wear, the nut can be adjusted periodically. The concern you may have about a wheel falling off are nill. The forces in that area are applied across the faces of the wheel bearing - not the spindle nut.