It seems dumb that poles are uncommon in an area with little topsoil over a granite substrate? Why so fancy? Incidentally this could mean that the trailer parks are cheaper to serve than swankier neighborhoods; there are lots of poles in trailer parks.
winter storms and strong winds. i've never lost power in the boulder area, except when a substation failed, regardless of the weather. when i lived in areas with overhead lines, power loss was a regular event, occurring during winds that would be considered mild in boulder.
Regularly trimming trees around the power line seems less expensive than boring through granite? The frequency of storm-related outages is a good proxy for how much the power company is spending on vegetation removal.
The front range gets 100mph+ chinook winds, and late spring storms dump feet of heavy snow leading to what we affectionately call "treemageddon", during which town will be filled with the thunder of trees crashing down for hours and hours. It's not an ideal environment for lines on poles.
at least in newer developments, my understanding is most underground channels (think sewers) generally provide some facility for running new lines/equipment in them, to reduce the number of times that city streets need to be dug up to lay x,y or z.
