The days of HTML’s primary use being as markup language for scholarly papers is long dead (and wasn’t alive for very long anyway).
Today, the web is a mixture of text, video, audio, and application. But the folks that make the video and audio content generally aren’t the same folks who script the pages, design the layouts, or write the code.
While it’s possible for a web team to make a website Level A and mostly-Level AA accessible without working with Digital Content Producers, the results are that much better when we all work together.
Creating Accessible Media by the GSA on Section508.gov