Novadays there're quite a few alloys which really can withstand corrosion even for such large periods of time.
As to why some of them have rusted and some have not, I can assume that the conditions could bedifferent - water vapor, gases, etc.
Now that was from a modern material engeneer's point of view.
I appreciate where you're coming from, but its hard to apply modern logic to elements of Nirn.
Another thing that I've often wondered.
Is there any texts remaining from the Dwemer?
Anything at all?
I'm currently trying to discover all of the ruins in Skyrim to find things.