it is CYA.
Like the Chinese radio trigger makers which effectively forced Canon into offering some degree of radio remote flash control the Canon EX-RT system uses the 2.4 GHz band which is basically free to use almost anywhere in the civilized world.
http://www.learn.usa.canon.com/resources/articles/2012/speedlite_600exrt_radio_basics.shtml
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Radio Transmission:
IEEE 802.15.4, ARIB STD-T66
Primary modulation: OQPSK
Secondary modulation: DS-SS
Sending frequency (center): 2405 to 2475 MHz
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Pocketwizard chose different frequency bands between 315 MHz and 434 MHz and ran into a lot of regulatory issues. Effectively they make 3 product variations for different parts of the world, which are mutually non-compatible and which may not be allowed to operate in other countries.
see
http://www.pocketwizard.com/inspirations/technology/frequency/
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North & South America and parts of Asia = 340.00 to 354.00 MHz FCC/US
Europe, India, China, and other countries = 433.62 - 434.22 MHz CE
Japan = 315.50 - 317.00 MHz
IMPORTANT, PLEASE READ:
PocketWizard radio devices operating on one frequency can not operate with PocketWizard devices on a different radio frequency. Retailers can not ship devices to markets that use a different frequency and we can not provide proper warranty service for products shipped out of their intended market.
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