Still, it's kind of underhanded to emphasize the "it's like the premium apps, but free!" as if it's some revolutionary new model... when in reality it's just the typical ad-supported version of an app that customers are familiar with. (The model may be new for developers, but the promotional page is entirely aimed at customers.)
I wasn't attacking them for claiming there weren't ads, sorry if it read that way. It's just that I read that entire page posted here, then went to my email and read the email they sent to developers, and I still didn't understand how or why they were doing this. I feel like they should have mentioned the word "ads" somewhere to explain how this would be paid for, rather than saying "actually free" over and over.
The promise is that there will be no payments for the app or for in-app purchases. Also, I've spent some time playing Angry Birds through Underground, and the ads seem much more unobtrusive compared to getting the "freemium" app through Google Play. I guess the philosophy is similar to the "Special Offers" on the Kindle e-book readers.