Thanks for that extra info, Steve. Having read that, I can come up with a few different theories.

1.) Perhaps they take power to the mic on a different conductor than the one used to bring back audio. That is really a better way to do it, from an electrionic standpoint... it allows them more leeway in where they set the operating point of the FET impedance converter, etc. (We'd need to find a schematic of the mic, or dissect one, to ascertain this.) Also, if the mic circuitry were designed well, this configuration would minimize the amount of electrical noise created by a slightly dirty connector.)

2.) Perhaps they keep the DC off the mic audio connector, so it's safe to use a dynamic mic without worrying that the DC would cause problems.

3.) Perhaps they just want to sell proprietary connectors and/or mics, by making it harder to use "standard" configuration mics. (I doubt this is the case with Canon, although Apple has certainly tried it and still does it on some of the iPud connectors.)

As you say... those are just guesses (but the first one is certainly valid from a technical perspective).

Maybe I should. I've wanted to be cheap about this, because these cams are going to be replaced. However, that doesn't help current students...

Of course the investment in the actual xlr cables & lavs would carry over to the next cams.