Currently Being ModeratedApr 2, 2013 8:33 AM (in response to Kerapsak)
The app has to be compatible for both devices. Do you have both of them set up with the same AppleID and iCloud account? They both need to be the same.
If a compatible app does not show up you can open the App Store on the device where it is not showing, click on Updates, click on Purchased, click on "Not on this i(whatever)" and then download the app.
Hope this helps!