Completely agree with you about things that are said with tongue in cheek. Some people just don't pick up on self-deprecating humour. That said, I still don't believe some of the stories on here, or at least I don't believe that the conversations are a true account of what was really said. There is a huge amount of exaggeration going on in the re-telling, to add weight to the accusations of snobbery, which might be quite flimsy otherwise.
I can tell exactly which anecdotes that applies to on this thread, because honestly, unless they are joking, people simply do not speak like that in the real world. It's like something out of a cheesy American film where they try to emulate things they think the British upper classes would say. It's all 'oh darling, how awfully, frightfully horrid for you, having to share a bench with a poor person, etc, etc. 
As an example, the story where a small child offered to share her lunch with the cleaner, only to be told by her mother 'don't be silly darling, the cleaner won't be used to eating quinoa.'
Well I'm calling it. That did not happen. I just do not believe it.
What might have happened is that the woman said 'no darling, that's very kind but the lady doesn't want to share your quinoa'
Or the woman said to the cleaner, in a jokey manner: 'I'm not sure you really want to eat my child's quinoa, do you?'
Or: the cleaner might have said 'Ooh yummy, what have you got for lunch there then?' to which the mother might have replied 'Oh it's just quinoa, have you ever tried it?'
Or the client was south American, where quinoa is a staple food, but something quite niche here, so she might have said 'I don't suppose you really eat quinoa, do you?' Referring simply to the fact that the cleaner is British, not suggesting that she is a total pleb.
None of those things would be evidence of snobbery, but the need to make it sound like that says more about the person telling the story than it says about anybody else. The main thing I took from it is that the poster thinks quinoa is a food only eaten by pretentious people.