Susan,
That was an interesting thread, and su.ki is quite authoritative in her knowledge of English (isn`t she a University professor someplace or something)?
Yes, certainly native speakers of a language are not taught pronunciation anymore than they are taught the grammar or vocabulary of their language. They just acquire it as soon as they start forming sentences.
I do agree that our brains tend to not only anticipate what a person is going to say before they even finish their sentence, which is why people interrupt one another so frequently, but unconsciously fill in sounds we expect to hear in words, even if in a song, or movie, that would otherwise sound distorted or muddled. I think it´s part of simply how we de-code sounds.
It all depends on how much familiarity we have with a language. Among native speakers of English, of the US variety, there are all sorts of muddled sounds that we can understand that are based on regionalisms that would throw off a non-native (mostly early) English speaker, even one with a high level of fluency. It´s a bit like anticipating what someone is going to say before they say it, based on the context.
Another thing I always keep in mind is that, in listening to anything on the internet or wherever, the sound quality could be poor, or the recording, or there could be any number of technical reasons why a sound comes out distorted sounding. So, maybe that´s got a little to do with it too.
The three THE pronunciations, based on whether the preceding noun starts with a consonant or a vowel, or whether you are using „the“ for emphasis, is a very subtle distinction that I doubt many Americans are aware of (maybe few Brits as well). I would bet that if I deliberately went around pronouncing „the“ as „thuh“ for any word, no one would ever notice or even hear the difference. It would be hard for me to do, because I`m not used to it, but I`d venture to say no one would hear the difference.