Yes, but when people refer to the U.K. as a region, they usually mean the U.K. (i.e. including Northern Ireland) and the Republic of Ireland. Ireland is seldom its own region.
There is no mention of the Republic of Ireland in their earnings report, yet their European headquarters are in Dublin. "U.K." in the report means the U.K. and Ireland.
Really? Where have you seen this? And what evidence do you have that Google's report isn't including Ireland in its "Rest of World" figures?
To include an entire country under the heading of another neighbouring country without making that explicit is a mistake, not an assumption, doubly so when Google have quite large (and distinct) corporate presences in both Ireland and the UK. It wouldn't be too far from Starbucks listing all Canadian and Mexican profits under "United States" when there's a perfectly normal term to describe the geographic region ("North America"), just as there is with the British Isles.
There is no mention of the Republic of Ireland in their earnings report, yet their European headquarters are in Dublin. "U.K." in the report means the U.K. and Ireland.