Why does XCode 4 include the file extensions and @2x suffixes in the image lists?

In previous versin of XCode and IB, when I would specify a background image for a button, the image lists would just include the filenames without the file extensions or @2x suffixes and the iOS was smart enough to know which file to use depending on whether or not the device had a retina display. Now in XCode 4, when I go to select an image for a button, it lists all the images in my project, including their file extensions and @2x suffixes. Which one do I use? If I choose the image without the @2x suffix, will iOS know to use the @2x version on devices with retina displays?

Thanks so much for your wisdom!