Building your own inftrastructure doesn't make bandwidth free, it just eliminates the cut that the provider normally takes.

Also, Akamai doesn't charge by the megabyte either, they charge by the megabit per second, as does most anyone once you start dealing with Facebook or Youtube-size loads.

When you peer, you no longer pay a 95th. You work out a peering deal with some provider you send a lot of traffic to and effectively connect directly to them in some shared facility. Some providers will charge you a 95th rate when you peer, but even then it's vastly cheaper than what you'd be paying for normal transit.

There's an "Akamai markup" which is a well known thing that Akamai charge for the heritage (somewhat analogous with the so-called "Mac-tax" except the Akamai "tax" is agreed to exist). A better comparison would be CDN pricing for Limelight or CDNetworks, the other two big players. It's worth bearing in mind that a lot of peering contracts for major carriers (but not necessarily Tier 1 - for example BT, Telefonica etc) depend on having a backbone - Akamai doesn't have a backbone, their backbone is the internet.

Also Google only do HTTP, so no Flash RTMP or Microsoft streaming which you effectively subsidise with an http product from a CDN.

Google also used Akamai for its Google Live broadcast which indicated that their network couldn't do RTMP (at the time).