I'm not a spelling/grammar nazi or anything, but seeing mistakes like this really puts me off things. Like, to the point where I have to close the tab because it annoys me so much.
I probably have a disorder. I should get help.
I don't think you do. Spelling mistakes on front pages tell me that someone didn't pay the kind of attention to their work that I would like them to. If their site is trying to sell me something, I conclude that their product is probably made with similar lack of attention, and that is what puts me off.
It's a bit like going into a restaurant and seeing the waiter not wash their hands after using the bathroom.