Photograph a scale to convince yourself.
Well, I guess I'll have to do that. Maybe. There seems to be a lot of confusion in the literature at large on this issue, and I think people lose track of the different reference systems they use to compare their understanding of the subject. Having a fixed, analog reference system (i.e. the 35mm film) made things easy to compare in the past, but in the digital world with different sensor sizes, different pixel densities, etc. it makes this discussion more difficult I think.
Anyway, it doesn't matter. I just wanted to find out if I could use the MP-E 65mm on my G1, and I think I got my answer. Thanks all! I'll just go back to taking photos. Cheers!