Re: When it comes to tubes,
GT has a pretty good sales machine, even though I think their machine was stronger in the 80's. Back then there were tons of ads for Groove Tubes in many magazines, even many magazines that had nothing to do with musicians.
People just don't know any better and want "new" tubes, not specifically the "right" tubes. Quite a large percentage of people will just buy what they can get their hands on. People also seem to trust their local stores in regards to tubes, for some reason. You are better off to go to a tube seller that sells many brands. When I see only GT tubes in a store, it makes me question their credibility.
Groove Tubes still has a strong brand name to newbies. It's a catchy name, and to a newbie buying from one company is an easy process. This is why Eurotubes sells so many of those complete kits. You can do better if you know what you are doing.
Older stores will sometimes always do what they have always done, and a catchy name from yesteryear may have more pull than an unknown new name to a customer. There may also be a price break to resellers.
Edit: edited manufacturer to company, which is more accurate.