That depends. If your quality if life is measured by nights out, it's true. However if I look back at my life my most satisfying and memorable happenings were either the ones I has to wait and long for, and the ones happened completely randomly - both completely irrelevant to going out or not on weekdays. Your life will not be less if you go out less - go out when you have a reason, a concert, a band playing, a movie you actually want to see, and not for the sake of going out.

BTW, I lived in London, public transport is not at all that bad; it's acceptable in Budapest, where I also used it quite a few times. If you can and are willing to afford a taxi, get a taxi, otherwise public transport is fine. (Not in Cambridge, though, there is no public transport in the night.)