As of me, I don't care if something that I did isn't marked, especially smart parts, patches, fixes etc. What I am interested in that something really _big_ (not huge but remarkable) will be marked, still (i.e., if I contributed a module which is new, my copyright will be there).
A seemingly minor, yet extremely important difference to understand is that authorship and copyright ownership are two very different things.
Having your name listed as a major or original author of a contribution is a much different thing than having "your copyright" included. If a grantback were instituted, you would assign your copyright to IDA (effectively making them the copyright holder) in exchange for the license to do anything you want with your contribution.
Bill