Why did browsers default to the miserable grey background? I just made this connection today while reading a page on the history of GUIs. Tim Berners-Lee developed the web on a NeXT cube (aka "great mudding box" or "worst print spooler in the history of earth"), and Nextstep, the OS, was predominantly black text on a medium grey background in presentation.
Steve Jobs was the founder and CEO of NeXT. I can't say with absolute certainty that Steve Jobs was directly responsible for the grey Nextstep interface, but he certainly wouldn't have allowed it to be released if he didn't approve of it. In other words, Steve Jobs is why the web started out grey!
[Admittedly, grey on black looked great on NeXT boxes because of their high resolution displays and fancy font rendering. Most other systems of the day lacked anti-aliasing and decent fonts, so grey on black looked horrible on them.]