When your audience is a broad spectrum of the citizenship of the United States, part of your mission is to communicate with them in a language that they can understand.
A movement within the federal government to help writers use easy to understand language led to the creation of the Plain Language website. There are some nice tips on the site for anyone who writes to a wide audience on their page about Usefulness in Web-Writing.
There's a column at the site of The American Society for Information Science and Technology (ASIS&T) on the development of the plainlanguage.com pages from one of the folks instrumental in its redesign of a year or so ago. One of the fun aspects of the redesign was that it was a project bringing together graduate students at Johns Hopkins University with the federal government.
The efforts of those students, and the feedback the site has seen has led to the creation of a new site, and guidelines for people who write web sites for the federal government: Webcontent.gov. If you're interested in usability and accessibility, this site is worth checking out. If you're interested in writing in a way which will make it easier for visitors to understand your message on your website, it's also worth a visit.