I think it's okay to retire games along as the game is in a finished state. For example, Tidalis, one of my favorite Arcen titles, is no longer being updated. I doubt that it would make enough money to cover the costs if they updated it. And that's okay. It's over.
I have Monday night combat, and I found the title really disappointing. It's just not a good game. But as I understand it, some people really like it, so, maybe it's done and in a finished state as far as they are concerned.
When it comes to Planetary Annihilation, maybe they needed to do a better job of transitioning to maintenance status or finishing features, but you can't expect investment into losing money. It's a business.