I believe, although I don't know for sure, that is why auto mfrs. have moved a lot of their assembly plants to the U.S. (obviously I am speaking of the Japanese mfrs.) Without the labor and retirement costs that some of the Amer. mfrs., they can produce cars relatively inexpensively here. Also, I would suspect the large volume of cars produced, especially in relations to bikes, helps keep the costs down. Obviously this argument does not hold water if you are talking about an Aston Martin Vanquish S, but it might if you are talking about a Toyota Corolla.
As for m/c dealers, my experience is that the service dept. is not always the cash cow everyone thinks it is. If the dept. is very well run, and is able to do a lot of work like performance or installing of accessories, often they cost money. Again, this is my experience.
Usually warranty work is a flat rate, dictated by the mfr. If it is something the dept. has to do a lot of, it obviously becomes less expensive the more they do. The mechanic becomes more familiar with the work and becomes more efficient. If not, then the dealership can lose money, because it is labor intensive, and the mfr. does not pay for how long it actually takes to actually do the work.
With regards to sales, it often depends on the unit. If it is a unit that is in high demand, then the dealer may be able to stick close to MSRP. If, however, the dealer has to compete with a large store (especially one with a large internet presence) , that is working off volume of sales, rather than higher margin on each unit, it starts to really drop the price.
It is a very tough business, and I see a lot of the smaller shops, especially the ones who have been around for a while, struggling. Add in the cost of keeping all of the inventory, and employees, and I suspect it becomes very hard. Again, I can only speak for my little world.