Wow, my bad! Thanks for pointing that out. If you scale my numbers up that would be costing you $60,000 per month. If you are doing recommendations you are probably processing significant amounts of data as well. I guess theres no way we could know the commercial arrangements, but It surely cant be the same as your average small time developer.
We also use Hive on Amazon Elastic MapReduce to do some of our analytics.
Our backend does much more than just serve static files -- you'd think that we don't have to do much but we keep track of video and exercise progress, summarize progress by user and by coach, provide video recommendations, host a Q&A system with notification support, award badges in real-time while avoiding costly datastore queries, handle mailing lists and email subscriptions, and have support for having a public profile to show off your progress, among other things.
We handle hundreds of requests per second and it's really nice to not have to think about scaling very much -- with any other solution, we'd be doing a lot more system administration.