You make it sound like porting an app from IOS to OSX is easy. Maybe you could write up a blog post or something for ignorants like me who would be interested in doing the same. Thanks for any additional details.
Some games might make the transition relatively easily. A game that relies mostly on single points of touch has a somewhat decent analog with the mouse, but only if it relies on certain patterns of finger movement. A game that, for instance, involves alternating taps on opposite sides of the screen, would translate badly—it's nowhere near as easy to leap that distance precisely with a mouse as it is with your fingers. Can you imagine playing the iPhone classic Dactyl with a mouse?
That kind of difference is present all over in touch-based applications, in differing amounts. It's up to the developer to find what transitions well and what doesn't, but in most cases it won't be a trivial task.
Prepare to be disappointed. Technology stacks aside, if the interaction models between desktop apps and multi-touch interfaces were in any way relatable, UIKit wouldn't have been invented.
If you want to write a Mac app for the new store, you'll be using AppKit.
http://www.cocos2d-iphone.org/archives/1074
The roadmap indicates mac support should be ready this release cycle (0.95), but it probably won't stabilize until 0.96. Once finished, porting games written with Cocos2d between iOS and Mac should be trivial, allowing for differences in input.
If anyone is interested in learning more about Cocos2d iPhone, I've started a tutorial series for people with little or no programming experience:
It's not finished, but I think it provides a good introduction to the basic concepts.