noseall, what you fail to see is that there is a difference between manufacturer and assembly. Honda "assemble" their engines. These engines are built from parts that are sourced to meet their requirements. You obviously have very little knowledge of the economical balance that these companies use. I'm guessing that you listen to everything that you are told and nod along with a glazed look in your eyes?
Example: lets take the daewoo nexia. looks remarkably similar to the vauxhall astra yes?! This is because they have purchased the rights to have the panels pressed by the manufacturing firm that pressed them for vauxhall before the body shape change. Now this is much cheaper than having to first build a factory, purchase machinery, employ research and development, manufacture the pressing tools (if you believe that they also make their own tools then god help us!!), then run the pressing plant and deliver these to their assembly line. This way the parts are delivered to them at the specification that they require without a mass outlay.
In answer to one of your previous questions about production of high and low spec parts produce at the same plant then yes it happens. It is down to the quality, thickness and type of metals used, the level of quality control testing done etc. It is performed as press runs and works something like Monday: Honda, Tuesday: Vauxhall, Wednesday Honda etc. (simplified version)
If you seriously believe that Honda manufacture every single part of their vehicles then you are very sadly delusional. Do they produce their own nuts and bolts too?? or how about their own welding rods?? or the fabric for the seats??!! I could go on for hours!!! If you really want the whole thing spelling out for you then i will by all means.
Oh and seriously, i would have thought that you, out of everyone, would understand this principle seeing as you drive a glorified Rover 200!!!! The 200 and the Concerto were both built at Longbridge on lines next to each other!!! They both have the same parts!! you could fit a Rover air filter and it would be identical!!
Now please stfu!!!