The default opener of a document is not the creator. Only the creator is the creator. Apple's "marketing" has nothing to do with it. As I have pointed out probably four times already, this is not a characteristic unique to Pages, it's OS-wide. And always has been. It's not my logic, it's Apple's logic -- you just haven't picked up on it before.
I think some of us are losing track of the purpose of icons. They are not there to create pretties. They are supposed to tell you something useful quickly and visually -- in this case, that the document with the generic icon belongs to an application you don't have installed on this computer. It may not be especially pretty, but it's accurate.
I still have to disagree. The purpose of an icon is to tell you what type of file you are going to open and what program will open it. It should only be blank if you have nothing assigned to open it.
If things are supposed to work the way you describe, why do .wmv files show up with a Quicktime icon? Quicktime didn't create them. In fact, on its own its not even capable of displaying them. Yet, the icon displayed for .wmv files is a Quicktime icon. And, Quicktime is an Apple product. So, the logic is certainly not OS wide.