I can't say what other brands require a dealer for service--your experience with Linn equip. is the first I've heard of that. A lot of mfgs. don't transfer the warranty on used gear, but will still service it.
One thing I do before buying any used gear is to call the mfg. with the SN & just ask a few basic questions, including date of mfg., & what their service rate/policy is. (The only mfg. that has ever gotten "snotty" about that & refused to discuss a used component with me is Krell). You can also glean a lot about their attitude & what it might be like to deal with them should you ever need service.
I also figure in the mfgs. distance from me, esp. with electronics (not so much with speakers), before buying used gear. For instance, I live on the East Coast, so right now I own a lot of C-J & Cary gear. And I've talked to both companies before buying used stuff & found them very helpful. VTL has been helpful over the phone also, but because they're on the opposite coast, I might think twice about buying a huge heavy pair of used VTL mono-blocs.
BTW, from what I know, Bryston is one of the only companies that not only has a 20 year warranty, but it's totally transferable, & their customer service is supposed to be excellent.