We don’t know — for any site. One reason we don’t know is because it’s difficult to detect assistive technology with a web server – and it’s arguably unethical to determine who’s disabled based on whether they use assistive technology. Another reason we don’t know is because the definition of “disabled” depends on who you’re asking and in what situation. There are a large number of models of disability defining who is disabled, and to what extent. If we start to define who in our audience is disabled, we find ourselves in muddy water quite quickly. The third reason is because when our website has inaccessible code, we’re actively blocking potential disabled users from visiting the site. That forms a vicious cycle: we don’t have disabled users because we don’t code for disabled users because we don’t have disabled users. Nicholas Steenhout illustrates this cycle in his article Why accessibility is good for business (according to my mechanic). Ultimately, it doesn’t matter. If we've got a public presence on the web, providing access to as many customers as possible is not only ethical, it makes good business sense. If we're providing services business-to-business, an accessible website ensures our customers don't have to worry about whether their disabled staff members can do their jobs with our products. Section 508 requires accessibility to sell in the US federal vertical, and similar legislation at the local, state, and federal levels in many countries requires compliance. In short, if even one disabled user is unable to use our site, we risk legal, social, and civil rights repercussions. Doing the right thing by making our sites accessible carries none of these risks.