You've probably noticed that SEO a subject that tends to bring out lots of differing opinions. Even experts feud on Twitter about which factors make up best practices. However, few will disagree on the importance of header tags, specifically the H1 tag, which has long been a factor for high-ranking pages.
How important is website accessibility? In the U.K., a blind man who normally uses a screen reader did a website accessibility survey and found that he was only able to access about 30% of all the websites he tried to visit. Purely apart from the social injustice, think about all the business those inaccessible websites are losing.