If you look at the article Dwayne linked, that compressor manufacturer is saying they really expect the product to start under a load that may demand more of the conductor than the code minimum. I also agree that MCC may be an off the shelf product that serves other loads in other places so simply the fact that they spent an extra buck on 6ga wire may not be important to this installation. I think that at the end of day, taking guidance from the manufacturer may be the way to go. Down here in the states we would say 110.4(B) trumps the minimum code.
