One of the biggest shocks of my life occurred in 1999, when I discovered this website. Game Music Online and VGMdb did not yet exist, and I certainly didn't know about JGML. There was a large (searchable) list of game music albums here, and I remember being particularly stunned at seeing Double Dragon II. My curiosity was piqued and I had to find out more (it took me several years to find DDII in mp3 format and a while longer still to find the actual disc). I next started to read the reviews and learned about these game series called "Ys" and "Final Fantasy", which I never paid any attention to from 1987-1999.
I want to stress that when I first found out about game music, it was not well known which albums contained arranged music. As an example, I had no idea what was on the Double Dragon II album. There were no reviews, and it wasn't until I browsed Quasi's server that I heard mp3 files. And it was arranged!
This hobby has few mysteries left. Because of VGMdb, most of these albums are classified. Newcomers are on easy street when it comes to information. I did not have such luxuries when I first started. I did a lot of work and spent a lot of money trying to understand video game music.
I am more filled with thoughts of gratitude that this market exists, rather than thinking about how to define it. Whatever this market is, it perfectly fit my personality type, since much of it was unknown.