From http://lists.w3.org/Archives/Public/public-comments-wcag20/2006May/0119.html
WCAG 2 violates WCAG 1 by listing an equation (for brightness as used in the [9]general flash threshold) as plain text. In so doing it pointlessly explains that ""the ^ character is the exponentiation operator."" I thought this kind of thing is what we had MathML for.
Because support for MathML varies across browsers and platforms, because the information from the equations can be mis-presented in some cases, and because it was possible to represent the luminosity contrast ratio in ASCII, a MathML version of the equations was not included in the guidelines themselves. We have, however, added a note to the definition which points to a MathML version. Should support for MathML change prior to publication, we will include this version in the guidelines themselves.