It may be done on purpose to keep the purple prose strictly black and white, header-sized text meaningful, and generally keep the aesthetic minimal, legible, and tidy.
If that is the case, we should honor the decision.
I feel bad even using bold, as if it should only be used on the original post. Sometimes I do it to the link text on a link, so it's a little more evident, because blue and black single-pixel lines don't differentiate too much against white.
You know how some forums are so MySpace-in-a-hot-mess looking. I am sticking to the basics.