Hey Oscar, thanks for replying.
I'd like to address your third point right off the bat, since it's the most important one: I didn't read your blog post. I stopped reading it after you spelled "itself" as "it's self". And, just like you said, it's because your grammar put me off. It's not that big of a deal to me, and shouldn't be to you, if you never intended anyone to read your post except for the person you were replying to. But if that was the case, why put it on a blog? If you want your blog posts to have the widest possible appeal, you should use standard spelling and grammar. It looks better, and it's easier to understand. No matter what your opinions on the relative importance of grammar, things like readability and aesthetic appeal matter. And if your work is not of a technical nature and is being published for a wide audience - like this blog post - they matter even more.
I'm not sure what to make of your point about your grandmother, since I'm sure you're aware that there are plenty of people with Ph.Ds in linguistics who would disagree with her intensely. I'm sure that a conversation with her would be interesting, and she might even change my mind, but the fact that she has a Ph.D wouldn't factor into it at all. My personal opinion is that spelling, grammar, and other elements of style are extremely important. The way that something is written has a major affect on the way it is received by the reader, and slight variations in word choice and spelling can change the actual semantic meaning of a sentence.
Using the "itself"/"it's self" thing as an example: Their meanings are not identical. "Itself" is often used as an apposition, which is how it would have been interpreted in the context of your sentence. "Its self", on the other hand, puts extra emphasis on the "self". Someone might legitimately want to spell it this way to emphasize both the phrase and "its self", which would be the phrase's characteristics. It doesn't read as an apposition, though, so the meaning is different. This gets right to the heart of what we're talking about: Using incorrect grammar has changed both the stylistic emphasis and the literal meaning of the sentence in such a way that makes it harder for the reader to understand. The reader shouldn't have to reconstruct what you meant to say out of what you actually said. (And, in any case, it would never be "it's self". Even following your grandmother's grammatical rules, you should have cut out the apostrophe entirely.)
As far as disorganized thoughts, that's fine when they're in your head, but when you put them on paper, you have to organize them. Organizing thoughts is what language is for.
Sorry for the looong post, but I wanted to make sure you understand me. I don't mean to attack you personally, but that seems to be how my comment was interpreted. A criticism of your writing is not a criticism of you. The main point I wanted to make is that style matters. It really, really, really does. I know you didn't necessarily mean for your post to climb to the top of Hacker News and get this level of scrutiny, but I hope you found the feedback useful. Don't take it too personally when someone criticizes something you write; it's just an opportunity to improve.