I disagree that maintenance is more difficult in London than in New York. I spent about two weeks in London about a decade ago. The first thing that struck me is that when you arrived at the tube station in Heathrow you'd get all sorts of information about which lines were in service that day. In trying to navigate London there was a constant shuffle about which stations or lines were out of service. Plus it took about two hours to get from Heathrow to Victoria due to signal issues (the wrong kind of snow is also an issue, apparently).