GAE is fast for things Akamai isn't. GAE actually has a more global foot print, because it has more peering agreements than any provider on the planet, and while you would be right if this was a CDN for pushing 1 Gig files, it is a CDN for pushing your 60k images all over the place. The cost of a Cache Miss on Akamai for a small file is VERY high, and nearly non-existent on GAE.
Building the right tool on the right platform for the right kind of job. (oh and pricing, You can't even get started with Akamai for less than $1000 a month, which goes a long ways on that pricing thing. Plus Akamai's 8-12 cents is not really 12 cents when you pay for storage, and all of the other nickel and dime things. CDN In A Box is just Simple Pricing, and Simple Deployment. ( you ever tried to write a blog post then upload the images to Akamai?)