From what I've read designers for web sites tend to have very high DPI monitors with high quality colour reproduction - so on their screens it is legible - and it seems they are so bad at their craft that they assume that is enough. What about the rest of the computer users who don't have the latest technology? What about those people with vision problems? Another point that is often brought up is studies that say high contrast (think black on white) is too harsh and causes eye strain. There doesn't seem to be a consensus on that though. If it is true the answer is to adjust the contrast slightly to prevent the strain not to reduce the contrast to the absolute minimum with slightly lighter gray on slightly darker gray background. Luckily Firefox has reader view.