[bluescrn]

Even the original Half-Life monorail intro sequence had the player moving relative to a moving vehicle.

You weren't moving on a simulated rigid-body physics object, but in practice there's not much difference - other than handling the nasty cases, like what to do when the physics object flips upside down and crushes the player, or resolving collisions with static world objects that the player makes contact with but the 'vehicle' doesn't.