Just yesterday I compared a VM with 8gb ram moving 4.4TB of data. With Linode you get 8TB for $80 a month. Yesterday AWS was $630 for the same server and the 4.4TB of bandwidth. For that price on Linode you can get 4 16gb servers, totaling 32 cores and 64TB of bandwidth. Even with the just announced AWS price reduction, it is still extremely expensive.
If you move a lot of bandwidth, check out Linode.
For starters, users that burn a lot of bandwidth probably don't do it by serving files from a VPS in a single location. In an AWS context, they may be using S3, Cloudfront and all the features and services that come with it. Setting all of that up on DIY VPS boxes (and maintaining it) may be fun for a hobby, but in business that's all costs. The cost of bandwidth is a trivial footnote.
Saying Linode's bandwidth is cheaper is like saying steak is cheaper at the butcher than it is at a restaurant.
I am not understanding how my comparison is wrong.
Not to say that you couldn't build a CDN on AWS, but if you're going to do it, wanting to do it for cheaper than someone who doesn't pay markup on the same instances (Amazon) isn't realistic.
You can move a lot of bandwidth for sure but as soon as you start using droplets or linodes for the sole intent of using its' included bandwidth (to self-build a CDN on it for example) you'll be shut down in no time.
On the other hand, if you have some heavy static files to serve, the scalability of S3 is hard to beat. It can serve the files more reliably than anything you can come up with.