[Robotbeat]

Indeed. This is because you get phase differences (due to finite speed of signal in wire, even though it's near c) over those distances. Converting to DC and then back to AC at the destination avoids any concern about phase mismatch.

[lbriner]

It isn't just that. afaik, a much larger issue is related to capacitive and inductive losses of AC. Even on the railways, an adjacent 25KV overhead line can induce a few hundred volts into the adjacent "dead" line, which is why they must be earthed before you can work on them.