Why would that be the case?
The reason we can cook and eat steaks rare is because dangerous bacteria form on the outside surface of the steak, and cooking the outside while leaving the inside rare destroys the bacteria. Grinding the beef mixes the surface of the beef with the inside, meaning you should cook the inside to 165F as well.
That's my understanding at least...
Ground meat on the other hand can introduce those harmful surface microbes to the rest of the meat, so burgers have to be cooked all the way through to ensure those microbes are successfully deaded.