The point was to make a clearly after-the-fact definition that works, but doesn't say anything interesting. There may not be any exocritters that use some other macromolecule for their genetic material. If not, it would be a non-issue, right?

It would still be an issue if we started making synthetic life. A good definition ought to cause as little inconvenience as possible. I agree that life isn't fundamentally different from all other matter, but the reason we have the word at all is because it's handy to be able to encapsulate it as a reference class. Individuals with a solid grounding in natural sciences may at least be at a state of "I know what I mean when I talk about it," but if we are going to define it at all rather than simply taking the Justice Stewart approach, the definition should encapsulate what we actually mean.