And the US is primarily serviced by either public utilities (usually owned by the city) or by regulated utilities that regulate the utilities including the profit margin, approval of capital projects, and other things. I.e., not any real reason for their to be a different between US and Finland in this regard.
I guess the real difference is a combination of the following:
1) general philosophy of, good enough, great is not required
2) Electric infrastructure is a little older on the average in the US
3) The regulation that exist probably more optimal for cost than service in the US in comparison.
Of course, cost is the reason why overhead lines are used. Contrary to what several posters have mentioned, maintenance cost on underground lines is actually usually higher on underground lines to overhead, but this factor is relatively minor in comparison to the significantly higher capital costs.