You give MacHeist's users absolutely no credit for being a diverse and multi-national group. Not everyone here comes from an English-speaking country, and many here have English as their third or fourth language (me included).
First of all, speaking personally, I want to point out that I'm not here to criticise anyone, least of all those whose native language is not English. The English language is one of my interests, and this thread of people's pet grammatical peeves therefore appealed to me. Call it anal or whatever, but some people take an interest in such things, and it's possible to have an entertaining discussion about it without implying any personal criticism.
I am a writer and former magazine editor (among other things) and I still spend a lot of my time working with words. From that position of experience I can say with complete honesty that I've used freelance writers from many different countries, and the thing that has generally struck me in doing so is how much better the quality of written English tends to be from foreigners than from native speakers.
Clearly this is hardly a universal truth. Some of my native English-speaking writers (from both the UK and NZ) were outstandingly good, of course, and foreigners (notably from Germany and Denmark) writing in English tended, understandably enough, to lack the easy flow and use of colloquialisms that one would expect from a native speaker. Nevertheless, if it was good grammar, good sense and generally high standards that I was looking for (which indeed it was), I found that I could generally rely on the non-native speakers to provide it, whereas the native English writers could frequently be careless and slap-dash.
To me, this says a lot about the relative quality of education in the UK and overseas. My experience of Americans is relatively limited in terms of editing their writing, and of course we are separated by a common language, so there are things that Americans consider correct that I don't like (and probably vice versa): such as my previous "lay of the land" example. My personal experience is primarily with British English, and the versions of English learnt as a foreign language by Europeans.
My other main point is that English is fluid and evolves constantly. Grammar rules are only a convention, and they change over time. For anyone who would like to know more about this, I would recommend reading David Crystal's The Stories of English, which is most illuminating (if a little heavy-going at times).
As with any argument, there are two sides: on the one hand, there are Grammar Nazis who lay down the law in black and white terms and say that such-and-such a usage is right or wrong, full stop. On the other, there are the people at the other end of the spectrum who don't know or don't care about grammar and spelling, and think that making oneself understood is all that matters.
Neither position is right. Personally I veer very much toward the Grammar Nazi, but I have to recognise the fact that we are dealing with conventions, and conventions that are not even universal. Conventions of spelling, punctuation and grammar change substantially within a single region over a period of years (it's easy to look back and see marked changes in the use of punctuation within British English literature within the last half-century, for example), and do not necessarily coincide between regions: American English is punctuated substantially differently from British English. (Note that, if I were American, I would probably have written: "American English is punctuated substantially differently than British English.")
To give a few simple examples, American English generally favours use of the Oxford Comma ("one, two, and three") whereas British English generally does not ("one, two and three"). But some British publishers insist on using it (not least Oxford University Press) and some American publishers insist on not using it. As a second example, British English makes a distinction between abbreviations and contractions ("Co(mpany)" would be abbreviated to "Co." - with a dot at the end - whereas "L(imi)t(e)d" would be contracted to "Ltd" - without a dot; American English would put a dot after "Ltd." because it treats the two cases as the same). Finally, the American use of "of" personally really annoys me a lot, because frequently it's omitted where it's clearly needed ("out the window" instead of "out of the window") and inserted where it equally clearly isn't wanted ("off of", which is totally redundant). But that's the convention that has arisen through popular usage, and is now 'correct' American English usage. The fact that I really dislike it is neither here nor there.
These are all conventions which boil down to being little more than publishers' house styles: you can consciously choose which to use and be 'right' regardless of your preference. As for other grammatical usages, they change over time, and dictionaries and rule-books are updated periodically not to set out what's right and wrong, but to formalise established convention that reflects how grammar works today.
So to be a true Grammar Nazi is to deny progress and refuse to accept the possibility of change. But that is not the same as saying that people should ignore the rules and pretend that they don't matter or that people don't care about them. As with most things in life, steering a middle course and accommodating other points of view is the best way to avoid problems. There are few absolutes, and grammar rules are no exception.
Born to the Purple