Because the GWR branch was part of your growing up experience, 7013, it is only natural then that it is a popular subject? Such solipsism! When I first read "Railway Modeller" in the 1950s, I got the impression that the BLT didn't exist outside GWR territory. The layouts (nearly all based on St Ives in Cornwall) were very attractive, to be sure; clean, dinky in size with nice rural scenery, and wasn't the "Bulldog" the prettiest engine you ever saw? Nothing like the scruffy mainline stations where I did my train spotting.
Nowadays, of course, the magazines tell a different story - yes, of course the rest of the UK had its branch lines too, and this is reflected in such gems of layouts as "Amlwch" (LNWR), "King Cross" (GNR/L&Y) and Oxenhope (MR).
But surely, 7013, you don't think that the only small stations with facilities for freight were those on GWR branches? From my landing window I can see the remains of one of the intermediate stations on the former GCR Woodhead route: this had a goods yard and coal sidings and links to nearby quarry, brickworks, scrapyard and processed food factory. Most of the stations on the line had some goods facilities, and this was true for nearly all the pre-Beeching railway. For a single track branch with a freight raison d'être, look no further than the KWVR, built to serve the woollens industry.
I agree with your basic argument, of course, but lets not make it all about the GWR!