You might expect a high level of accessibility from a site called Usability.gov. You might be disappointed. Sadly, I wasn't particularly surprised by my quick look into the accessibility of this site.

Age is definitely a factor. While the copyright is up to date, the fact that has custom style sheets for Internet Explorer (IE) 5 and newer, and 4.7 and older makes me think it's not a new design. With that code, I'd hope it was more than five years old. Regardless, it's showing its age.
Some of the low points of the site are:
- Absolutely horrible use of headings for structure.
- Use of images of text rather than text.
- Bad use of the hover pseudo-class making navigation awkward
- No use of the focus pseudo-class making keyboard navigation all but impossible
- An unreasonable number of validation errors and warnings
- Invisible skip links, which don't work in IE.
This is one of those sites that seems to pass most cursory accessibility tests without actually being accessible. It follows the letter of Section 508 compliance, while throwing the spirit of the law out the window. That it does have skip links, but you can't see them and they don't work is a perfect example of this. It has the appearance of accessibility, without actual the benefit of accessibility.