Have now come to expect mistakes on websites etc as the rule not the exception, right from the smallest of small businesses, to pretty much the top end.
For me, it goes beyond that I'm bothered a firm can't spell or punctuate; in this context, I'm bothered you don't pay a tiny bit of attention to getting things right, given all the spellchecks & whatnot available. Firstly your website just says amateur the minute I see a slew of errors, and second I think - why would I believe you take care over what your actual business involves, if you can't do a quick proof-read?
I am reconciled to the idea that most people don't notice or care, so it probably doesn't even harm business, but is that a good enough reason to lie down & let it roll over you? Occasionally I'll correct someone & very occasionally they appreciate it; but I imagine many probably wouldn't, or would thank you to your face & mutter 'who cares, nitpicker..' to themselves.
I'm not just talking the odd typo btw, this is everything from a self-publish firm that can't spell, to blurb that's practically gibberish, to glossy magazine sites getting names wrong, &c. Plus I'd need a whole other thread just for sites that can't sort their navigation so that key stuff is findable, or is even ..there.
Losing battle..?