*shrug* Doesn't mean you can't get a more accurate rhythmic notation out of the x/8 signature. All swung 4/4 is (as far as I can tell) is a way of making a 12/8 rhythm easier for high schoolers (or others who haven't worked with 12/8 nough to become fairly proficient) to read quickly. Seriously, take a swung song and play a 12/8 check pattern behind it. It fits better than a 4/4 duple rhythm.

It's just a pet peeve of mine in music that the correct time signature (a function of the beats and subdivisions of the music, not necessarily the composer's choice of time signature) be used. I understand the convention in jazz is to write in swung 4/4, but I say "Why bother?" in the marching setting. We've got a time signature that works (for all intents and purposes) better as a vehicle for rhythmic accuracy than swung 4/4 ever could. My biggest question is (commonality aside), "What do you actually gain from writing in swung 4/4 over 12/8?"