To play devils advocate Dan... and support Nick and my own personal thoughts... how many people have been killed or injured when overhead lines come down, poles hit by cars... ice storms etc... (I won't say tree limbs falling on lines out loud.. oops.. ammo for Clearance)
I'm sure high voltage transmission lines are cheaper above ground, but maybe not.. and the risks associated with living within proximity... hummm...
It is possible to build underground systems and make them work.. it's being done all over the place... it's just easier in pre-existing areas to put them on poles. I would love to see a twenty-thirty year study done by an outside auditor of overhead vs. underground installation and maintenance costs.
We have digressed of topic here I believe, but one thing has come out of it... complaints of clearance contractors and the quality of work done in maintaining the required set-backs... I do not have a lot of clearance experience, some, but it is far from my major... However, I would say two things regarding poor quality work, primarily I think it can be blamed on the service provider, rather then the contractor... sure they are the ones doing the work, but if it's not up to par... "Corrections", hold back of pay, loss of contract, it's not that hard. The bids are generally (around here) awarded to lowest qualified bidder, well if X tree company didn't perform last time because they were taking short cuts to get the contract finished, they are no longer "qualified” then eventually contactors would get the picture.
The utility contractors need to enforce harder, it can be done, and the pruning can be done right.... oh yeah and STOP PLANTING SILVER MAPLES UNDER EXSITING WIRES!