this isn't really a big issue thanks to Microsoft Word, however... how much work and money would it take, to add a spell checker to the main site? also this is 2017, one would assume every active site by now, would have some kind of spell checker, at least for the English language. or am I oversimplifying this?
You can use the Grammarly browser extension which should be available for the most common browsers. Besides spell checking, it also shows several grammar issues. As it is a third party tool which is quite widespread it will be more accurate and powerful and doesn't need any maintenance. I suppose that there are also similar grammar/spell checkers for other languages available.
You also have to consider that most Internet browsers have built in checkers(Although you have to turn the one in firefox on every time) From what I have seen most of the people who post stuff with really obvious spelling mistakes instead of just grammar mistakes would not take advantage of a built in checker. Since as I said, odds are they are using chrome which checks automatically anyway.
