The NY subway is also able to run 24/7 because of redundancies in routes, so they can perform maintenance without the subway stopping. London doesn't have this option.
Worth pointing out that there are redundancies in some routes, not in others. Sincerely, L train rider :)
Yeah service to Williamsburg is still dicey. You can be a sardine on the L, or if you're close enough to the JMZ, you'd better not have to ride back after 8pm (one or more of the trains may not be running).