That's a completely different kind of game. Roguelikes are single-player games, MUDs are multiplayer games. Roguelikes usually feature permadeath, MUDs rarely do. It's the difference between an RPG and a MMORPG.
Also Nethack offers a turn based top down gameplay simulated with ASCII chars, MUDs are real time or almost real time based with a wall of text and prompt based, like a text adventure.
I don't think anyone plays MUDs with plain telnet. Just use a client with an automapper like tintin++
Or kbtin.
On top of what others have said, the advantage to using one of these remote versions (besides removing the need for a local install), is that they often provide support for arcade-style features like leaderboards and the ability to watch other players games either live or as replays.