If you look at my post ( 3rd down ) on this stack overflow page, you'll see that my code isn't highlighted. Even though my code is indented by 4 spaces, I had to use the <PRE> tags around my code to get mono-space font. If you take away the surrounding <PRE> tags, the code is interpreted as normal text, even though it is indented.
It was in a list. In a list you have to indent it by 8 spaces.
Rich fixed this by adding a rule before the code, to effectively separate it from the list.