The Play Store has a spot next to each device in your list for an image of that particular phone or tablet. This whole time it's pretty much only been Nexus devices that had the image instead of a generic white outline. Now all of a sudden almost all phones and tablets have an image, which looks much nicer.
Most of the notable devices you might link up to your Google Play account will have a device image, although both versions of the Moto X are still missing, and a few of the images are really low resolution. This is a substantial change, especially considering it took Google months to even add an image for the Nexus 5 after it was released last year.
There's no functional difference—it's just a nicer look when you send apps to devices.