Really, the problem is the rule. It should really say "A creature can take a free action to use an attack power that isn't normally a free action only once per turn." Free Action attack powers are inherently limited--they specify how often they can be used, or are used based on a limited and very specific trigger. It's only when you have multiple properties or powers that let you make lots of attacks on a turn that things become a problem--and that's typically because of abilities that let you use -other- powers as free actions.