Not everyone has or can afford Microsoft Word though. I hear it's now standard with Windows, but I use a Mac. Of course, NeoOffice is an open-source program under the GNU license that has a similar spell and grammar check. Even then, the grammar check is just that--a grammar check. If you spell something wrong, and it happens to be a part of speech that works, it won't detect that. (There are a number of mistakes in that last post, by the way.)
I think this grammar and spelling rule is a flexible one though. It's not like someone is going to get punished if they forget a comma before a preposition between two independent clauses. (I hope this isn't the case...) The problem is that English has THE most complex rules of any language, so much so that people with doctorates in English might not know them all or at least not remember them all as they write things. In addition, English varies from region to region, and there are even disputed rules, such as the Oxford comma or the recent expansion of the preposition to the adposition. It would simply be too much to ask if everybody had perfect control of English and knows every rule up-to-date.
Have there ever been any encounters here with people who capitalize every word? I Don't Understand Why People Do This. It Looks Even More Disruptive Than No Capitalization At All.