Yep, I was consulting for a firm with an already sizeable infrastructure investment/dependence on AWS, and their architects were proud of their best practice usage of multiple AZs for redundancy, but weren't know that inter-AZ traffic cost also. So I imagine they're going to have fun trying to incorporate that into their infrastructure layout.
In my day job we saved $600 a day by cutting down on needless inter-AZ traffic.
Its amazing to me that this is all included for basically free except for Application level filtering by these providers.