There was a big change going from winkeyless to the one with Windows keys. I've not seen any difference between cases after that other than the colour. There are Win-key keyboards that support different protocols, so obviously those must have been different controllers: AT, PS/2 - USB-combo and USB only.
AFAIK only the electronics on the controller board changed ... but that doesn't mean a different keyboard case does not exist.
Where did you hear that they have different current draw? I've measured the current draw of a USB version. Enabling a single locking LED made it draw three times as much as idle, so they are really only comparable when all LEDs are off.