I think saagarjha's point was that an even simpler standard would be for the creating application to use file metadata to annotate the files. And a simpler standard is generally more likely to be followed, especially if it's unilateral.
This doesn't help with installation, obviously, but it helps with cleanup.
The classic MacOS had exactly this concept: Creator Code[0], similar to the Type Code[1] but storing a file's creator rather than its "mimetype".