They are not making new installers just to give you a circle icon. There has to be a reason they are bothering. And it has already been noted some of them do have substantial changes added.
If they bother to change something, they ought to document the change and flag it on the shelf for easy identification. I do not think that is too difficult to do but I do think it would be better customer service.
It's not just the icon. It's a new version of the installer program. It installs to a different location by default outside of program files, doesn't have the integrity check on smaller files, has newer games in the installer ads, digital signatures etc
I agree that there should be some kind of changelog for when they change things, although the game specific forum usually has a post by staff if they do.