But it sounds to me like the core argument being put forth is, to carry that analogy forward clumsily, that the infrequent coffee shop customer is entirely different from the coffee shop customer who sits in the shop and that he complains about stuff that no one else does...
Nobody but you said "entirely". I'd say something more like, "substantially, and in ways you may or may not realize".
i.e. the guy who only takes his latte to go is saying that the location of the chairs in the store is bad feng shui, while the people who stay and drink there never discuss this or observe this as a problem.
More the other way around - the guy who pops in on Mondays to get his lattes to go is not going to care about the chairs, as he doesn't use them. The chairs are inconsequential to him. The folks who are there for several hours a day, however, will care very deeply about the chairs, as they are the ones with their butts in them.
And maybe that'll translate into a discussion of chairs, or maybe something tangentially related to chairs - like the flow of traffic through the store, or how cold the shop is (because the chairs may be grouped near the exit), or what have you.
Moreover, the folks who are in that coffee shop every day are... hanging around a coffee shop, shootin' the breeze. The Monday morning latte set are not. This says some things about each - MMLs are either more busyaat those times, or just don't like sitting around in coffee shops, while the regulars have the time and inclination. That speaks to having different concerns, in general.
Also, the regulars quickly develop a certain amount of groupthink, history, and common ideas that the Monday morning latte set haven't heard about. The Great Bean Controversy may mean a great deal to the regulars, who lived through so much of it and saw the fistfights, while to the MML people it is apt to have meant that a couple of times they came in and their coffee tasted a little funny, and at which they shrugged and moved along.
No, take this one step further, and realize that most folks aren't even MMLers. They never even enter the store! They live in other states and cities, and your little store means squat-all to them. Anything even vaguely particular to the store is apt to mean nothing at all to them.
My experience has been that such discussions happen in person just as they do online (though perhaps the frequency and vehemency of the discussions vary) and that there is no hard and fast rule either for the discussion or the commenters.
Yes, well, in my experience, most of the discussions seen here almost never occur in a gaming group. For example, the term "GNS" theory has never arisen at my table. We have never had anyone given a beatdown at my table over 3e/4e preference. Only one of my gamers regularly also runs games, and he does so with a different set of people altogether, so no "GM theory" discussion ever happens among my folks...
Your (or my, or Piratecat's, or whoever's) personal experience is, honestly, just like experience on a particular forum - it is experience with a small subset of gamerdom. Any small subset can (and in fact, is statistically expected to) have notable differences from the usual behavior of the whole. You have to specifically go out of your way and take precautions to select a small subset that does represent the whole reasonably well. This is the reality of statistics, upon which most of the science that supports your technological lifestyle is based. I wouldn't dismiss it lightly.