No, it's the technology or perhaps the companies supplying it (unions are only ever a problem in the US - or maybe they're never a problem and there's only a propaganda system against them in the US). London Underground are currently in the process of literally the third attempt to upgrade the signalling on the subsurface lines (i.e. including the District) - the previous attempt by Bombardier failed outright (as London Underground were aware it would from the early days, but they were politically obliged to wait until the company admitted as much), and the one before that (a similar story with New Labour ideology-driven PPP) was also abandoned.