I think that's generally true. While it's not like you can easily get to every corner of the British Isles or Western Europe generally without a car, there's a lot you can do out of Dublin or London with public transit and maybe the odd cab ride. Generally good as Boston's public transit system is, other than taking the train to New York City, flying somewhere, or taking a bus to someplace that is mostly not very interesting without car transportation on the other end, your options are pretty limited beyond what's covered by the greater metro transit system.