While you're correct that in this way a CDN is similar to peer-federated systems, this is also a low-effort trite response that misses about 70% of the differences between the two.
The main difference being, of course, CDNs provide a delivery and storage service which you pay for, meaning the content remains yours, the circumstances under which it is viewed is under your control, and you're simply paying for them to deliver it for you. With peer-based systems, those two key points are no longer true.
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While you're correct that in this way a CDN is similar to peer-federated systems, this is also a low-effort trite response that misses about 70% of the differences between the two.
The main difference being, of course, CDNs provide a delivery and storage service which you pay for, meaning the content remains yours, the circumstances under which it is viewed is under your control, and you're simply paying for them to deliver it for you. With peer-based systems, those two key points are no longer true.