-Every single Mac user 10.7 & 10.8 has the Mac App Store on their system.
-You already have 100% of the work done.
-It's free advertising and exposure.
-It will give you a primer to the app store approval process for iOS.
-It's only $100 to be a part of the program.

We submitted to the Mac App Store and were declined, a couple of times, for various policy reasons that require us to make very significant changes to the Mac installation. We'll approach them again, but not right this second.

Looking at the 2013 app store review guidelines, I can't see how some apps are in the app store. I see you're probably violating like 5 of them. Maybe you guys should talk to Spacetime Studios to see how their MMO update system doesn't violate the same rules.