Robin Payne:
I tend to beleive the more probably explanation that the Southern
Railway took suburban commuters seriously as a market, and provided
frequent, electric commuter trains. The other 3 of the big 4
basically ignored this market...

I tend to believe this one as well. And I'll add that the reason behind
the reason is that London is in the southeast of Great Britain -- so that
lines running north or west from London could carry lucrative long-distance
traffic, but other lines could not, because there were no long distances.
The southern railways, and later the Southern Railway, *had* to concen-
trate on short- and middle-distance traffic, because except for one line
to Exeter that competed with the GWR, that was all there was.

The GNR, of course, not only had its long-distance traffic, but *did*
go after suburban traffic in a big way as well, building branch lines
in north London -- and they came to regret it, calling these services
their suburban incubus". In the end, this added to the growth of tube
lines in north London. First the GN&CR and GN&SR were successively
promoted as ways to relieve the GNR, then abandoned to eventually become
parts of the Underground (also the former, of course, didn't stay one);
then some of the branches were handed over to the Underground as extensions
of the Northern Line.
--
Mark Brader, Toronto "'Run me,' Alice?"
-- Tom Neff

My text in this article is in the public domain.