I understand the sentiment (and we'll be improving the overall contrast issue), but just saying the font should be black doesn't help anyone. White is still the overwhelmingly most popular background color for text online, and nobody is doing black text on white; this also becomes uncomfortable for many readers. We(I) made some guesses about what looked good on our test devices, and it turns out the general consensus is it should be a little heavier and a little darker. Certainly not black, though.

See also: http://www.ironicsans.com/owmyeyes/

Although with proper line spacing and font size and a lowered contrast the effect is diminished. People tend to lower the contrast too much or don't set a comfortable line spacing.

The problem?

Most people don't read their own site often enough.