I almost bought the wrong 6D today...didn't know there were differences

This factor is at work with flashes, too. Members have posted that they bought a 600EX from a dealer in New Jersey, only to find that it lacked the radio trigger feature. Some countries prohibit some electronic features, so Canon makes dumbed-down models for those markets. This is not just a camera thing; consider the motor vehicles that are not available in countries with the most stringent rules regaring safety or pollution-contol equipment. For example, I would love to own a certain model of Land Rover, but the USA will not allow its importation, because it has no air bags.

Some dealers, such as B&H, are honest about their grey-market items. Others leave the grey-market factor unsaid, or will be deceptive.

I am not ranting against grey-market items. An educated buyer is what is important. I have recently considered a certain grey-market item, myself.