I cannot comment on BMW, but speaking of service and etc. costs here, in Belgium - I had Hondas, Suzuki, worked for friends on Yamahas and Kwaks and there is absolutely zero service price difference between Triumph I have now and good deal I had on Honda. I really do not know where this opinion comes from, perhaps from way local business takes advantage of "cool" factor behind European makes.
More to it. KTM - not any more expensive to service etc.
Yamaha probably is the most expensive and Kwak is worst on parts supply.
Honda are expensive to service unless you have really good dealer.
Parts not cheap either.
So, I think that making assumptions based on each personal experience into common rule won't work here.
Example? Easy. 130 Euro asked for carbs sync on Honda from my friend and 50 Euros asked from me (because I know exactly what and how they will do it and know dealer guys well) for exactly same job on exactly same bike of exactly same year. This is reality. But in my place.