But that is not a fair comparison either. Bikes are cars are as different as pie and cake.
With a bike you have a frame. Then you have a bunch of 3rd party parts. If lets say Fuji makes a road frame and then a few years later that exact frame is made and branded motobecane, there is no difference. Now, Fuji might have used some R&D money and made a better frame in the meantime, but the two frames in question are the same.
I am not fully agreeing with the poster above in that all these frames are a few year old frames of big makers, but some are.
Then the rest is not rocket science. A 2008 Shimano XT RD is a 2008 shimano XT RD, regardless of what bike it is on.
Cars are groups of very complex systems. It is not like Audi makes a frame and then Shimano makes industry standard transmissions that all cars can use, or Fox makes suspensions for all cars.