Using U-Verse, I can download the file even using my default DHCP DNS server, and using Google's 8.8.8.8.

It does seem strikingly similar to a problem I'm having (http://forums.att.com/t5/Setup-and-Self-Install/Weird-issue-connecting-to-att-idns-net/m-p/3199325), though, which leads me to wonder if AT&T has some weird routing problems that are not network-wide with their content delivery network.