Some greenhorn is hired by Fly-By-Night Electric and gets sent to a big commercial job. His foreman tells him to do something, say, "Run ¾" rigid from here to here for this 480-volt circuit." The poor cubby, not wanting to do all that work, says, "Why can't we just use EMT? I know how to bend that, and it doesn't need threaded." To which the foreman just says, "You can't run 480-volt in EMT."
What the foreman doesn't expound on is that the job specs prohibit EMT on the site due to it being a classified location, it's a vibration issue or any number of reasons why on that particular job, or in that particular portion of the job, the specs say to use rigid. So from then on, the newbie thinks the NEC prohibits 480-volt circuits in EMT.