To keep drifting for just a moment, a glance at the Google map of Cornwall gives comparable results:

Truro, Porthcurno, Poltesco, Perranuthnoe, Germoe, Gunwalloe, Traboe, Perranzabuloe, and Trevescoe.

I'm getting beyond my depth here, but Cornish and Welsh are both varieties of the Celtic language spoken in Britain before the arrival of the Anglo-Saxons - and for some time afterward. That language is called "Old Brittonic" or often just "British." Another descendant of British, Cumbric, was spoken in Northern England and parts of Lowland Scotland. (Gaelic seems to have originated in Ireland and not to have come to Britain till the 6th Century, by which time Pictish - very possibly another descendant of British - was apparently well established in northern Scotland. Sorry for so much hedging, but the written - and carved - evidence remains scanty.)

So going out on a limb, my guess is that the "-o/-oe" place names in Scotland and Cornwall - and elsewhere? - are ultimately holdovers from British

I hope someone will tell us if they have better information.

Though not necessarily on this thread.