According to iLounge, the ABC player flat out refuses to work displaying a message that says, "Please connect to a Wi-Fi network to use this application. Cellular networks are not supported at this time."
They also note that YouTube is displaying videos at a "dramatically lower resolution."
AT&T has indicated that the downsampling is not their doing. "Its just a question for Apple."
Business Insider's Dan Frommer has since tweeted that the ABC is wifi only on purpose. I believe rights play a role. (theyre different on wifi vs 3G) sounds dumb but true. abc told me the decision was based on a variety of business and technical considerations. but no details
[Engadget] [iLounge] [TechCrunch]