I don't think it would be correct to assume that this is limited to the monk only, especially when the text is question really isn't making any new rules ... it's simply clarifying to the player that a monk only has special rules for "off-hand" attacks when the monk is attacking unarmed (or with monk weapon); otherwise, the monk suffers the same penalties everyone else does. The response singles out the monk simply because the question singles out the monk.
So if:
1) Monks suffer the same penalties as everyone else when using non-monk weapons and making off-hand attacks
2) Monks are allowed to make an off-hand unarmed attack when wielding a two-handed weapon
I don't think it's to much of a stretch at all to assume any class can make an unarmed off-hand attack when wielding a two-handed weapon. So a fighter using this tactic would do two-handed weapon damage + base STR with his primary attack and 1d3 + 1/2 STR for his off-hand unarmed attack.
Slander