I'm not quite sure whether there was ever an original source for this claim other than a bunch of tech blogs parroting each other, but iSuppli shows that this was false, at least as of July 11th:

http://www.isuppli.com/Teardowns/News/pages/Low-End-Google-N...

Sure, if you add in the $25 Google play credit, and leave room for some margin for Asus (since Google is just a reseller), you might get close to breaking even, but as far as I can find, the Nexus 7 was never sold at a loss.