But if Rackspace is the ISP, and the ISP presumably has other customers, doesn't a DDOS often affect other customers of that ISP? I think so. Rackspace would have to mitigate the attack, no fair trying to charge one customer. Unless they took on a well known target customer, that is.
Let me tell a story. Some years ago (long ago, really) I was working on some antispam stuff.
There was a popular free DNSBL that was being DDOSed all the darned time, this affected people's mail, including my customers.
Since it was a free list they had little money to do high cost anti-DDOS stuff. Understandable.
I contacted one of the big distributed hosting providers, a name you would know.
I asked one of their top people if the company would agree to provide hosting for that DNSBL, for the good of the internet. As a way of helping. The processes involved would be a tiny blip for a company their size. Others would maintain it, they just had to allow the queries. A tiny blip of DNS lookups for incoming mail.
I got an immediate response that this was an interesting request but they couldn't get involved in anything that would draw unwanted attention from bad people, because it could affect their shareholders. Understandable.
I responded that I would appreciate them helping but I understand. And how long would it be before they were themselves targeted and extorted by criminals? I got no response.
It wasn't long, I think less than a year they did have some criminals attempt to extort them under threat of DDOS. It was in the news.
I am sure they were able to handle it internally, they were big and had a big distributed system. But this just shows, you have to help if you can, or what happens when they come for you?
Like I said, I understand they don't want to take on a known target. But the stuff in the OP was nothing like that.