[BlueTemplar]

Mods can be released anywhere, but in practice, usually aren't ! Steam might not provide hosted MP servers for non-Valve games (are you sure it doesn't ?), but we've even seen older games having Internet multiplayer removed to the exclusivity of Steam's own "VPN" : Dawn of War 1, Civilization 4 (for which they also managed to break most mods for no seemingly valid reason)...

[mrr54]

In practice mods are definitely released outside of Steam Workshop. I don't think I've ever used Steam Workshop for a Skyrim mod for example.

[BlueTemplar]

Skyrim had mods before Workshop even existed. Things are very different for games released with Workshop support.

[mrr54]

In my experience they aren't different at all. Steam Workshop is just a distribution platform for mods. It's a mod installer and manager. It doesn't stop you doing it manually.