No, you don't need them....
UNLESS you want to re-scale your (iPhone) graphics when an iPad user "zooms" the display. When the iPad user changes the application zoom level, you can receive this notification:
_UIClassicApplicationWillChangeZoomNotificationName
And use the appropriate graphics, or on your views, layers, etc. set the drawing scale
// scale just changed!
CGFloat scale = [[_window screen] scale];
[layer setRasterizationScale:scale];
[layer setShouldRasterize:YES];
It's entirely optional. Some views have custom graphics that look terrible when scaled up on an iPad, this can fix that for you.