>>It amazes me to see how many power lines run overhead in the USA and Canada. To me it seems funny to have, say, traffic lights hanging from cables strewn across the road. Over here all power goes underground after the cross-country pylons bring it into the main sub-stations. There aren't so many telephone lines coming from telegraph (as they're still called over here) poles anymore even (our street is quite exceptional but, being Victorian, there is no under-road infrastructure other than the drains).
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>I suspect this is one of those cases where size is the big issue. North America is just so big that the difference in cost between running above-ground and underground cable is probably huge. It also may be related to when the cables were first put in. I also suspect that in much of North America, the cables were there before the inhabitants. (That is, electricity and phone were strung across huge spans of area to connect places that existed and then folks settled in between.)

As I've heard from the technicians who eventually came to fix the lines (and they weren't local, borrowed from North Carolina), the main reason is the cost of investment. It costs a lot more to dig the cables in than to just hang them. But then, this is Virginia, where you have a combination of coastal winds and lots of forests, so any stronger wind fells down a few trees, and even a category three hurricane (like Isabel was) left about half a million people without power for days. Probably the cost of crews doing the repairs isn't negligible, and revenue lost also isn't, but that didn't affect the bottom line at the time when the lines were laid, and may as well be covered by insurance to some extent.

When we were buying the house, we checked first - and the cables in this area are underground. However, we're connected via some poles on one of nearby main streets, and when one of those was hit by a truck, we were without power most of the day.