website design - Is there a problem with using black text on white backgrounds?

Why do a lot of websites use a text color other than #000000 black when the background is white?

For instance, this text will be displayed using a dark grey:

.post-text {
   color: #333;
}

Have some studies been made on that topic?

Answer

High contrast such as black on white can cause eye strain. Also there is evidence that it is particularly bad for people with dyslexia. For further info read articles at UX Movement and The Bristol Dyslexia Centre.

WCAG provide details on what is acceptable colour contrast, but dont state an upper limit. Personally, I like to use a different algorithm that provides an upper contrast warning. For further info, see this article at Spider Trax: "Does W3C Get Its Contrasts Wrong?"

Slightly off topic, but check out Contrast-A, a good tool made by Das Plankton for picking accessible color schemes.