some offer the same app to work on both devices(called universal apps)
if you see that +, it means universal, no + and its specific to that device.
if its iPad only, it will not work on iphone.
but 99% of iphone apps will be able to work on iPad and look like this, but they are adding the requirements slowly to make iphone apps universal(via updates to the app).
there is an option covered by that right hand just below, that will show 2x, that will stretch the app, but not high quality(high definition) that you are used to.
Most of these iphone apps, via jailbreak can make them fullscreen, by adding a certain tweak "fullforce or retinapad".
only have to buy an app once.
but example...slingplayer have an iphone app and iPad app, that you have to pay twice, cause they didn't make their app universal, not very nice.
i don't see others doing this.