what do you think thy are, they are wirless networks. Please show one example where a complicated sequence with hundreads and probably thousands have been used like that.
With so many buildings in line of sight of the towers you could even use microwave bursts to detonate the triggers.
Movies use complicated remote controlled effects sequences all the time, often with buildings, etc. in the way, this aspect is pretty trivial I dunno why your making such a meal of it unless you really don't even want to consider the possibilities.