S3stat's nightly job takes about 60 hours to run, and it needs to start and finish between 3am and 6am every morning. Amazon kindly keeps 20 machines ready to do that for me and only charges the time I'm actually using them. That's pretty amazing, and well worth the price in my mind.
So yeah, if you need a box to run your webserver 24/7/365, you can find a better deal elsewhere. But that's really never been what EC2 is for. To continue the example, S3stat.com lives in a cage at a colo since, as the author points out, that's a much better deal than running it on EC2.