I was also wondering about greater london suburbs, and whilst there might be a straightforward "just do whatever feels like it's most useful and least confusing to site visitors" answer, thought this might be worth floating for views. Taking Surbiton as an example I think well known to several prolific posters, currently it has 27 open pubs, of which only one is in an area, Long Ditton (I suspect that may have happened because of unexciting reasons to do with the administrative and postal boundaries not marrying up) and that feels a bit silly. We could either (a) get rid of the Long Ditton area and just keep everything under Surbiton, on the basis that it's not a very big area and 27 isn't a great deal of pubs that actually needs dividing up further, or (b) divide the rest up into areas.
The most logical way to divide up, thinking about distances between pubs so it might be useful when planning a crawl, and also based on generally accepted area names might be to have the following areas:
Tolworth - 5 pubs
Berrylands - 5
Hook - 2 (this could also pick up a couple of Hook pubs that are in Chessington postal town, if you can do that)
Long Ditton - 1
Surbiton Town, or Surbiton Town Centre - 17 pubs
which adds up to 30 as there are 3 pubs I'd put in two areas because they're somewhere in between.
Lots of people on the river side of Surbiton have been calling their bit 'Surbiton Village' in recent years, and would doubtless prefer that, which would potentially take 7 pubs out of Surbiton Town and into a new area of Surbiton Village. Though I'd be inclined not to do that as (a) Surbiton Village isn't a generally recognised description, thus could be confusing (b) there's not really enough distance between them to make this a particularly useful distinction when e.g. planning crawls (c) you could get into an argument over whether 3 of the 7 pubs actually qualified for inclusion in the 'village', and (d) there is a school of thought that 'Surbiton Village' as a concept only reflects some of its residents being completely up themselves.
Finally, one could put one of the pubs in an area called 'Seething Wells', which they make much of on their website, but that would seem to be a ridiculous distinction to make on this site.
Whilst writing, I'm coming round to my original thought that doing whatever feels best might be the simple answer.