Joined: Feb 2012
Posts: 19,353
Likes: 5,471
From: Rochester, NY
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
Actually not all top/lock nuts are capped. Most are but some Asian ones have had a "rubber" seal acting as the cap portion and are easily removable. Also some cheap US made top lock nuts have had no lip or cap.
As to why- I suspect it's a nicer look thing. Andy.