Dyn comes in on the other side of the equation. You use your ISP DNS server (or Google's 126.96.36.199, etc.) to look up addresses. But the people running the servers have to publish those addresses somewhere in the first place, and to do so, some of them use a service like Dyn.
To use a simplified phone analogy, Dyn publishes a phone book and your DNS server is 411. If you call 411 and the operator can't find the right phone book, they can't give you the number you want.