This is Priority One unless the information is non-important to the webpage. If the information in the applet does not affect the purpose of the site then this isn't such a high priority. We just need to make sure that the information is provided to everyone through these applets can be accessible to all. As we follow these guidelines then we can provide more traffic to our websites and more people will buy and browse our products or services.
The ONE checkpoint associated with this guideline says that programmatic elements like scripts and applets must be directly accessible or compatible with assistive technologies. It's important to provide accessibility to applets and java This checkpoint can be priority one if the functionality of the element is important and not presented elsewhere. Otherwise, it is a priority 2 recommendation. It is also important to remember that if the script creates motion then developers should provide a mechanism to freeze or stop the motion.
Source:http://www.w3.org/TR/WCAG10/#gl-own-interface