We need to make sure that all of our content is correctly spelled, and not just for accessibility reasons. It's rather embarrassing to be using a unversity website where they misspell the word unversity (which happens all the time). As a user though, when you look at a word you tend to correct the spelling and fill in the missing letters. It's easy to understand the meaning of the word, correctly spelled or not (for example, did you catch that university was misspelled earlier in this paragraph?).
Misspelled words create additional problems with accessibility. Screen reader programs speak the words on the web page based on the rules of the English language. When a word is misspelled, those rules go out the window and while the screen reader will attempt to correctly speak the word, it may not be intelligible to the user. So in this case, what the user hears could be way off from the meaning of the word as intended.