Beware that having a good connection with some servers on the Internet (Ookla's SpeedTest servers in your case) doesn't imply that you'll get a good connection with all servers on the Internet.
If anything, every ISP will make sure it's properly connected with Ookla's servers, because it's some of the most popular link test out there, and they obviously don't want SpeedTest to give them a bad press, otherwise their customers would go elsewhere.
I can tell that something has been off with PSN download speeds since FW 2.0 (in the sense that they aren't as stable as they were before), but it also looks like Comcast is one of those greedy ISPs who try to racket content providers besides already getting money from customers.
So, I'm not sure what or who is to blame here...