Internet Explorer is a universal product used by people young and old, new and experienced, speaking many different languages. A lot of people take advantage of IE’s built in accessibility features (like page zoom, caret browsing, find in page, etc) and additional assistive technology such as screen readers to use the web. Accessibility is beneficial to everyone no matter what their abilities.
As with every Internet Explorer release, we are committed to delivering a browser that’s accessible for all users. Part of achieving that goal is making sure assistive technology works well with IE. IE9 fundamentally changes how users interact with the browser and how the browser takes advantage of the entire PC. Those changes also impact how assistive technology interacts with IE, which necessitates updates from some assistive technology. For example, the new notification model is not read by many screen readers, and screen readers can no longer depend on the GDI display subsystem since IE9 uses Windows Direct2D and DirectWrite as part of enabling hardware-accelerated HTML5.