In the upload pages, the text
"Allowed Extensions: sit tar.gz tgz dmg hqx bin cdr iso zip sitx img"
could be modified a bit, like (I believe)
"Allowed Extensions: img sit hqx bin tar.gz tgz
Mac OS X games only: dmg sitx
CD images only: cdr iso zip
Please modify my suggestion for other non-Mac standards, like tar.gz, tgz, iso (when are they useful, for example).
On the other hand, I know this will not be recognized by uploaders.
We recently got Chessmaster 2000 in a zip format, which is useless for games created for Mac OS versions up to 9.2 (anyway, I replaced it with an useful format), just because Mac OS versions earlier than Mac OS X can't handle them.