The articulated screen is what G12 and G11 makes them very good for normal family outings. I've taken a lot of pictures using my G11 at extraordinary angles. The articulated screen isn't what sets G1X apart from the rest of the G-series. It's the sensor. Canon should restore what has been introduced before for the G series. Besides the optical viewfinder, this articulated screen is what sets it apart from the S series. Actually, I would rather have an articulated screen than an optical viewfinder which doesn't even have any AF point to begin with and too small for an average adult to use comfortably.
I'm not disagreeing, I'm just observing that that is what Canon has decided to do with the lines. I love the articulating screen on the G1 X. But they chose to remove it on the G15 and G16. Thus, the screen and the sensor are both premium features on the G1 X, with the drawbacks being added size, slower lens, worse close-focusing and autofocus. If they add the articulated screen to the G17, people will complain about the added bulk (or, if it remains the same size as the G16, the lack of slimming it down). I doubt they'll do it unless they decide not to replace the G1 X (which is also a possibility).
As for what sets the G series apart from the S1xx series, other than size, I don't know.