Pheace: You can see some of that reflected in the response they gave for AOWIII Linux build not being released DRM-Free:
Yeah, that's a good case in point. Sadly I think the number of developers in that position is on the higher side of things, where the extra effort is dramatically disproportional to the potential number of customers to make it an unbalanced commitment of their resources both up front and for ongoing maintenance. There is an additional problem that occurs when considering ports to non-Windows though too, and that is any middleware a game might use. If a game makes extensive use of various middleware and even one of the dependencies is not available on the particular platform customers desire a port on then it can be essentially difficult to impossible to economically do as they're more or less held hostage by the lack of portability of the middleware. The only viable option for such games might be releasing a port via winelib which isn't really a true port and more of a second rate release strategy that often is considered less than stellar at best or outright crap in many cases. Relying on such middleware dependencies holds software hostage to the platforms the middleware supports which is unfortunate. I think this might be one of the reasons why Witcher 3 isn't available for Linux for example.
popperik: Wasn't Age of Wonders 3 day one? Hmm...
It appears so. Not sure if that would fit into the AAA category or the more broad category of well known mainstream games though. I guess it can be rather difficult to categorize some games in this manner in a non-ambiguous way though. I'm interested in seeing more of both categories come here though and both are potentially equally as exciting. I imagine it would fit into a similar category to Divinity Original Sin and Dragon Commander perhaps though.
It would be interesting to try to come up with a metric to carefully delineate the games which is easily testable however I imagine that would be impossible to do easily. :) Having said that, I suppose such suggestions are equally welcome in the discussion as they can be just as exciting even if they aren't the next Far Cry/Battlefield/Call of Duty/Starcraft class of game per se. There's definitely some breathing room in the definition. :)