Normal people care.
With words is how the world communicates, it's really basic stuff and makes people look like retards if they don't know how to use basic year 3 or 4 words that are used daily. I know plenty of companies/businesses/organisations including the one I work for that would shred your job application if it contained basic mistakes like that, obviously it probably does not matter when you daily work schedule entails around feeding and milking cows.
Again there is a difference between making a mistake or making a typo and not knowing the difference between your and you're (stuff you should have learned in year three or four), which are two completely different words with completely different and unrelated meaning.
There is a massive difference difference between 'knowing your shit' and 'knowing you're shit'