I've been doing a bit of research to try and get to the bottom of all the different OEMs. Some of these are still on the market, so hopefully this is useful to somebody.
Basically, the main difference from the "bad" keyboards (like the iOne Scorpius U9BL) and the "good" keyboards (like the Max Keyboard Nighthawk series) appears to be this: Full N-KEY Rollover over USB, onboard memory, and a PS/2 connector. These are the features that indicate different internals.
The following are "bad" keyboards -- (identified by: no full N-Key rollover with USB, no onboard memory):
iOne Scorpius U9BL (apparently known as XArmour instead of Scorpius in some territories -- literally the same keyboard, both are branded iOne, although it seems that they're often mistaken for being two different keyboards)
Whereas these are "good" (identifiable by: full N-Key rollover with USB, onboard memory):
Max Keyboard NighthawkQPad MK-85Rosewill Apollo RK-9100xRFinally, I came across a third one, which is different to all the others:
Monoprice 9181This only has 64-key rollover with USB -- so clearly has different internals.
Externally they all look completely identical -- apart from the lack of a braided cable on the iOne model -- but they're clearly very different internally.
Contrary to some of the posts here, I would find no evidence that the QUMAX Xarmor U9W (which is actually a Wireless keyboard) or the Razer Blackwidow (which is completely different from what I can gather) are the same to any of these.
Happy to be corrected on this, but hopefully my research is of some use!