After writing the post below, I got to thinking. Go read that one. Then come back.
I wouldn't want anyone to think that I subscribe to the idea of 'proper English'. I don't.
I have a friend who's much older than me. When he was young he was told to speak 'the Queen's English'. But is this really about speaking the same language as the Queen? Or is it more about speaking the form of English that people of his parents' generation were familiar with?
Australia for a long time tried to be like a piece of England that had been set adrift. Part of the mechanism for this was denigrating any other forms of English. But language is a living thing. It grows and changes. It evolves. Unless it's a dead language like Latin. Or a stillborn one like Esperanto.
When groups of people leave the 'motherland', wherever that may be, they take with them the form of their language that they know. Often they keep that form, while the country they left behind changes - and so does it's language. Australia has many remnants of a form of English that's no longer spoken, and now seem perculiarly Australian. At the same time, words have entered into the Australian lingo that aren't from England at all. The Australian accent in some places bears the remains of Cockney because of our convict history (this shows especially in our rhyming slang). In other places it's a touch more Scottish. Where I come from, it's a very 'proper' form of English. People I meet when I travel around Australia often don't think I'm Australian at all - especially if I'm travelling in the company of a Westie from Sydney.
This brings us to the Americans. I've read in a couple of places that the American accent derives in a large part from the time that America was settled. This means that if you took a modern English speaker from England, and a modern English speaker from the US, and put them both in a time machine and sent them to Shakespearian England - the American would sound more like Shakespeare than the English person would. In terms of accent, at least.
And Shakespeare is the classic example of the evolution of language. It would be folly to try to calcify language and keep it forever the same - it's virtually impossable. The people whinging about the corruption of the English language by youth are fighting a losing battle. But they fight it just the same, because they aren't comfortable with modern usages.
I must admit here, that I'm not comfortable with some modern usages, and some changes. But that is because they are unfamiliar to me - I didn't grow up with them, and occasionally I don't understand them. It's not because I think that English should always and forever more sound and look exactly the same as when I grew up. Words change their meanings, and new words emerge. Spoken language changes a lot faster than written language - which is why I can understand this, even though I find it hard to read. I may not like it, but I can't stop it. That's also why I don't get the shits up with young Aussies who write ass instead of arse. I could bitch about it, if I wanted to waste my breath. But I don't. American English is just as valid as Australian English or the Queens English or Aboriginal English.
I still think it's useful to learn to write with commonly accepted spelling and grammar - for the same reason that it's useful to learn table manners, even if 99% of the time you eat in front of the TV with the plate on your lap. Some day, for some reason, you might need to know.