I work for Cloudflare, and we do not charge you money for our DDoS protection. It's free and included on every plan level including our free level, and the protection you get is equal to the protection our enterprise customers get.

In other product features we have we also work hard to make sure we do not charge you for any bad traffic, i.e. our HTTP rate limiting product has the pricing structure designed so that you aren't paying for the traffic stopped by it.

Pricing really isn't the issue here, but where Linode and other hosts adding DDoS protection helps is in the scenarios where your origin / host IP or provider is known. In those scenarios attackers may directly attack the host.

Just as elsewhere in security, you are as strong as your weakest link, and I am really pleased to see hosting companies expand their DDoS protection.

The various disclaimers: I am the engineering manager for DDoS protection at Cloudflare, and I run a little farm of machines at Linode :) I'm happy on both fronts with this announcement from Linode.