Currently, there is no cover art displayed for Internet streaming stations. The latest beta of iTunes also removed the feature completely and replaced it with Apple's alternative, so hopefully that will change by GM.
Dear Internet Radio Provider,
The iTunes Store now requires cover art for Internet Radio stations. The cover art files must be 1400 x 1400 pixels in JPG or PNG format using RGB color space. The image URL must end in ".jpg", ".jpeg" or ".png". To add cover art to your station, send an email to firstname.lastname@example.org including your contact name, station name and cover art file.
Cover art should avoid pixelation. Any text should be legible at reduced image sizes on small devices. Note that Internet Radio cover art is not currently displayed.
Questions about iTunes Radio?
The iTunes Internet Radio Team
iTunes Radio will launch with iOS 7 this fall, and it is still unclear what Apple will do with its current list of streaming services -- however this recent email indicates it plans on keeping them around and perhaps bringing them to iOS 7.