If they own a house, make at least 100k a year and can support their family comfortably, I would consider that wealthy. My father is in this bracket and he goes on vacations over seas, owns 3 relatively expensive vehicles, and still saves enough for retirement.
You don't need a million dollars to live a rich, fulfilling life.
I've never actually heard anyone call it X before, unless they were making a joke about the whole thing. Everybody I know still calls it Twitter. Calling it X is just embarrassing.