Nobody is saying that PokerGo should be as robust as Netflix. I know that a completely ridiculous argument like that is easier to attack, but I don't think you need to resort to that.
The fact that it's a common feature means it's a reasonable thing to ask about. Maybe he's considering signing up. It's just kinda weird to assume that he's hinting at piracy.
The main issue with your post was suggesting that there's no fathomable reason to legitimately want offline viewing. If you're actually standing by that claim, I encourage you to take a moment to think about it a little harder.
Or, if you just didn't know that was a thing, that's cool too.