It is what is is. I guess it's hard to do right. Your scenario is obvious enough, but MS needs to think through a lot of business scenarios and it can become complex.

Beyond all that, this may be what you need: msdn.microsoft.com/en-us/library/ms461526.aspx

One rational argument for how they have done it is to do with records management. Had your attribute change  routed the record  a different way, perhaps into a folder with a different disposition policy to the base document  content type, you would end  up having a disposition occur on a document to delete it, and another record exisitng that had a dependency upon it. Hence, no delta's in versioning  as they cause issues with ummutable versions.