As many people are complaining it seems that in the Apple SDK for the Retina Display there\'s a bug and imageWithContentsOfFile actually does not automatically load the 2x i
Ok, actual solution found by Michael here : http://atastypixel.com/blog/uiimage-resolution-independence-and-the-iphone-4s-retina-display/
He figured out that UIImage has the method "initWithCGImage" which also takes a scale factor as input (I guess the only method where you can set yourself the scale factor)
[UIImage initWithCGImage:scale:orientation:]
And this seems to work great, you can custom load your high res images and just set that the scale factor is 2.0
The problem with imageWithContentsOfFile is that since it currently does not work properly, we can't trust it even when it's fixed (because some users will still have an older iOS on their devices)