Yes, there are two 'flavors' of the 600EX - one with radio triggering (-RT) and one without. Availability is geographically restricted, so in some markets only one is available. For example, in the USA only the -RT version is sold (or at least, that's supposed to be the case - someone reported ordering a 600EX-RT from a 3rd party seller on amazon.com, and getting shipped a 600EX non-RT - meaning ripped off, since they paid for the -RT and got a grey market item lacking that feature instead).
AFAIK, it uses the 2.4 GHz band, which is what's used for 802.11(g) wireless. Still, some countries restrict those frequencies to specific types of devices, and while it's possible that Canon could have sought regulatory approval for the RT flash in those countries, that approach was deemed more expensive than developing another version without the radio.