Honda has a similar following, so it isn't just the Germans.
Very true. Honestly, any performance car will have its fan base and store directed for parts. When I had an SRT4, I was part of a forum just for that car and there were websites selling everything you can imagine for the car. It just goes with the territory. The reason you're going to see more for these cars is because of how many years they've been around for.
Though with that in mind, so does Honda and Civics... They probably have even more parts than you can imagine because of how popular they are and the price in which you can mod vs the power you get from them.
I guess yeah, as excited as you might be to think Germans are the only one that do it, they're not. Switch car brand and you'll be surprised.