There is a small folder inside the minecraft/bin folder called natives. This folder contains files that have platform-specific code. When you copied over your install, you copied over the Windows-native files in this folder. As a result, the game fails to run.
You can fix this by replacing the contents of that folder with the correct files from a valid 1.4.6 installation that was done on a Mac.
I'm not entirely certain how you can do that, but the files from a 1.4.7 install may work if in fact Mojang have not changed very much except for some classes in the main jar file. Archive your modded install somewhere else, install MC 1.4.7 fresh, and save the natives folder it generates somewhere convenient. Wipe the rest and put your modded install back in place, remove its Windows-based natives folder, and drop in your new one. See if it runs.
If using a 1.4.7 natives folder doesn't work though, one way to try would be to use Minecraft Nostalgia, which can downgrade the latest version of Minecraft to an arbitrary previous version. (I've used it for downgrading to 1.2.5 for modding purposes, but I haven't done it on a Mac. It appears to support Win/Mac/Linux though.)
You would safely archive your modded install, wipe it from the minecraft/ folder, then run the vanilla launcher to get 1.4.7. Close it out, then run Minecraft Nostalgia, choosing 1.4.6 from the list. Once it's done the conversion, grab the minecraft/bin/natives folder for later. Wipe the rest, put your modded install in, and delete the minecraft/bin/natives folder that came from Windows. Finally, drop in your natives/ folder gleaned from MC Nostalgia, cross your fingers, and launch!
Again, I've never had to do this, but it should work.
Best Answer
This is because you're computer does not handle minecraft's way to change fullscreen in-game. Its to complicated to explain since it envolve code.