I found another odd thing on OS X. I compiled a program using the Release option, with all debug information off. It seemed unusually large, ~7.7 MB, so I ran strip on it. This got it down to ~4.6 MB.
The Windows and Linux executables were both small, so this seems to be happening only on OS X. I don't mind running strip, but this seems like a bug.
Cheers,
VTwin