The mathematical notation you see on this site is generated by a WordPress plugin called LatexRender, which uh, renders LaTeX formulas.
LaTeX is a mathematical markup language used by scientists, mathematicians and engineers. Since it can’t be embedded in HTML directly, a tool such as LatexRender is required. It converts the LaTeX markup into something that can be embedded in HTML — images. Each formula is rendered as an image which is embedded in the text of its containing article.
As good as the LaTeX notation appears on this site, you may notice that it isn’t as perfectly typeset as it would be in a journal article, for instance. This is particularly true for articles delivered over RSS, which have more obvious alignment problems. That is the compromise with having to turn the notation into images — there is less control in matching the formulas to the containing text.
Can LaTeX Formulas Be Left in Comments?
No, at least not for the moment. It could be enabled, but there are some implementation issues. If there’s sufficient demand I will consider it.