Nigel: How does the development of Manx surnames relate to that of Irish surnames ? - the early Stanleys rulers had seen service in Ireland and might well be used to Irish names - did this influence the names - if Manx names derived as you suggest from place names/decriptions then did the same hold true in Ireland eg Dublin area had seen similar Norse influence.
In the 1428 Garrison roll there are very few Manx names - one is McGilcist (Gilchrist), another is McAlex (mc Alexander) which would possibly tie in with Moore's derviations