Yes, that's a good point.
I was lucky with my trumpets...neither had any reliability issues in over 36,000 miles of riding. The TEX only had paint peeling on the front of the engine casing...everywhere else was mint. I must have been one of the lucky ones as plenty of others have been plagued with TC/ABS and engine management issues. New ones seem to be worse than the Mk1 Explorers! More to go wrong. In truth, BMW reliability is no worse than Triumph when you look at how many reported faults are spread over the forums. Again, I was lucky as I dealt with Cheltenham Triumph who imho are one of the best I've come across and take customer service seriously. Some others it seems don't provide the same levels of service.
Cotswold Motorrad have also been excellent. How they react to out of warranty issues remains to be seen but I guess it will depend on what it is. It's not reasonable for example to treat the ESA as a consumable on a bike out of warranty but which may only have covered under 20K miles. You'd reasonably expect to re-valve any unit or replace it at perhaps 35K miles. Ditto....extensive corrosion on a 3 or 4 yr old bike that has been cared for is not a reasonable expectation.
As you say, whether you stay with the fold does depend to a large degree, on how the dealerships treat you.