A habitable zone is simply defined as the region which is most likely to be able to sustain the conditions for life in the form that we know of it.
Of course we don't know if other chemistries of life are possible, but that doesn't mean we can't define a habitable zone based on what we do know and expand it later if necessary.
As for looking at moons far from the star, it's barely a reliable means of confirming liquid water even within our own system, good luck detecting liquid water on an exomoon orbiting a far out exoplanet.
Mars is in our habitable zone and has plenty of evidence of having had liquid water flowing on its surface. The evidence of it having had conditions which could sustain some Earth-like life on it has only been increasing, making our current idea of habitable zones pretty promising. The fact that it currently doesn't have any liquid water on the surface has little bearing on that.
Of course we don't know if other chemistries of life are possible, but that doesn't mean we can't define a habitable zone based on what we do know and expand it later if necessary.
As for looking at moons far from the star, it's barely a reliable means of confirming liquid water even within our own system, good luck detecting liquid water on an exomoon orbiting a far out exoplanet.
Mars is in our habitable zone and has plenty of evidence of having had liquid water flowing on its surface. The evidence of it having had conditions which could sustain some Earth-like life on it has only been increasing, making our current idea of habitable zones pretty promising. The fact that it currently doesn't have any liquid water on the surface has little bearing on that.