Light colored text on light background - Why?

[tgonhawk1]

On so many websites, for reasons that I cannot fathom,
text is presented on a white background, using a gray - sometimes very light gray - font.

The middle line above is the default (and it appears only) color on this forum, which isn't too bad, but isn't great either.
I have seen many sites which use fonts akin to the top one - light gray.

My question is ... WHY? ... The poor contrast with a white background is just hard to read.
What's wrong with good old stands-out-from-white-background black?

If anyone can enlighten me on what the merits of light-colored text on light-colored background are,
I would be ever so grateful.

 

[tgonhawk1]

Here are some examples from the Hawkhost.com home page:
These are reduced from full size.

This is the original presentation - gray color, titillium-weblight font:

This one changes the text color to black:

This one changes the font to Verdana, and boosts the font-weight on the next and previous markers,
which are VERY hard to see without that.

And for good measure, this appears just below the reviews section: gray text on gray background!