[TIMOB-1747] iOS - displayCaps returns unexpected value on everything but iphone 4

on a 3g/3gs/ipod touch (4g or older) = "low"
iPad = "high"
iPhone4 = "high"

expected:iPad and 3g/3gs/ipod touch should be "medium", retina displays to return "high"

script snippet for repro:

var win = Titanium.UI.currentWindow;
Titanium.UI.setBackgroundColor('#FFF');

var label = Ti.UI.createLabel({

width:"auto",
height:"auto",
top:10,
left:10,
right:10,
text : 'value goes here',

});

label.text = Titanium.Platform.displayCaps.density;

win.add(label);