Is it at all possible to open a 3rd party iPad app in a mac (xcode emulator, for example) Someone asked me this - I think the answer is no for a number of reasons, but I wanted to confirm. Is there any way to open an iPad app on a mac desktop or laptop?

For example I download a publisher's ipad reader - call it the WSJ's, for example - could I run it on my iMac and buy issues etc?
You can't. IPAs downloaded from the App Store are built for the ARM processor in actual iOS devices. The iPhone Simulator is not an emulator and can't run ARM code. You will need to compile your own app from the source code, so unless the app is open source you will not be able to do this.