Daleana: What may be confusing you, Cais, is the fact that several states have passed laws that make sexual orientation a protected class. The Federal Government, however, has not. The argument is that the things that are considered Federally "protected classes" involve physical characteristics that are so readily apparent that you can be judged on them immediately. In order to know for sure that someone is gay, you have to be told. You can't just tell by looking at them.
I actually listed the states that have employment protections for sexual orientation (and in some cases, gender identity). The Shepard Act will be a huge step in achieving protection federally, I think; that is in addition to protection in federal employment (narrow protection, anyhow).