[Nymeria]

That is definitely not true for all MUSHes. Take Elendor, for example. Their combat system supports a wide array of weapons, and there are associated stats and skills (that can be trained up), and it can most certainly affect the outcome of battles and lead to the death of PCs. However, the system is never used on its own without roleplay.

While our CharGen includes setting stats and skills for all characters, our game does not have what I would call a full combat system (yet), but we do have coded systems for jousting and for melee combat in tourneys. These systems are used to determine the outcome of such events, so that can certainly affect the game. We also have skills that play into our rumor system, since social intrigues and politics are a big part of the setting, and there are many games (World of Darkness games, for example) that make use of +roll systems for a wide array of skills.

How much or how little you can affect the game world on a MUSH depends entirely on how it is setup. We follow known canon events on our game, so there's a limit to what can happen. But MUSHes that use original themes can allow quite a lot of changes at the hands of players.