There's also an object page for Mech. I think their blurbs are quite different:
Robot: "A
mechanical lifeform, typically exhibiting superhuman abilities, that
can be found in games as either the main protaganist or as powerful
enemies or allies."
Mech: "They must be big, they must have legs (but not always), and they must have cockpits. That's a Mech!"
While I don't really agree with the tone of the Mech's blurb, the two do show a clear difference.
Edit: I bolded the more important differences.
Edited 5 months ago