Well, that's one take on how commerce is intended to operate. Personally, when I walk into say, Curry's, and purchase a product off their shelves, I expect the same quality of support and customer services from Curry's for any product sold, regardless of who the manufacturer might have been.
If Matrix intend to provide widely different levels of support for different games, ignoring some while posting daily regarding others, then they should say so on the site and when you purchase. At least that way I would know whether I want to buy here or at Gamersgate etc.
Quality of support is a key channel differentiator in a competitive market, particularly when consumers have multiple channels to choose from.