Ed, I respectfully disagree.
The definition of mag is actually
-2.5 log ( \int Ftarg(lambda)T(lambda)dlambda / \int Fstd(lambda)T(lambda)dlambda )
where T is the transmission curve which can be quite broad.
This is important, because the inversion depends on the spectrum of the source
("color correction") and therefore if you pick a simple conversion and just
give the number in Jy, you have lost information. So it's more than just
the compression efficiency that you describe.