I personally like the limitation of the raw metal finish - it keeps a tight constraint on the cost factor and is in keeping with ethos of these types of devices, given we have become so accustomed to 'flash surface exteriors', it makes a statement about these devices part in the history of product development - bare metal is a statement and a 'living' finish.
How you present that is another matter.
If it is coated it adds cost - and that can actually add a chunk to unit price. If the metal is of a corrosive type one could opt for economical hand coating with something like CorrosionX or one could go the other extreme and use corrosion as a form of protection and get a nice red coloured 'patina' to the framework ! ;-)
Possibly move to a metal sheeting that has a zinc coating... and still keep it 'raw'.
Nice Day.