Captain's Crankarm length

Is there any reason that the length of my crank arms, as captain of a tandem, should be longer than the crank arms I'm comfortable with on my single bikes? I can't imagine there would be. But a local dealer for one of the leading tandem builders tells me that all tandems the builder makes come with 175mm crank arms for the captain, regardless of the size of the tandem. That sounds crazy. What am I missing?