I decided, why not ask those who know, so I emailed engineering at RHC. Gas_producer was spot on. Here's the note I received back:
"Hate to disappoint you but the answer is a lot simpler than your theories.. .The reason the pre-takeoff check was reduced to 75% was purely to reduce. .noise levels and be neighborly.. .Regards,. .Kurt Robinson"
Guess that means that if there aren't any nearby people to offend, Vorticey could keep doing mag checks at 104% afterall. <img src="smile.gif" border="0">