That is poor advice which doesn't account for the difference between computer screens and ink on paper. The deepest black you can get on a monitor will not be as dark as certain inks on a page.
I'd argue that it does account for that difference, just not in an immediately obvious way. Screen displays are an additive color model and print is a subtractive one; screens shine light at you, paper has light shined on it. This makes for a very different perceptual feel; (completely) black ink on white paper is way less "contrasty" than #000 text on an #FFF background. WCAG accessibility guidelines suggest a minimum contrast ratio of 7:1 luminosity -- #000 on #FFF is a 21:1 contrast ratio!
In practice, I think we'd be better off darkening the background a little and lightening the foreground just a touch; #333 text on #F8F8F8 background still "feels" like black and white, but (assuming you've chosen a reasonable text size) it'll be a lot easier to read if you're dealing with long-form text.
I find it difficult to believe that the relative difference between #F8F8F8 and #FFFFFF matters at all relative to the the widely varying screen brightness settings on everyone's very different computers, tablets and phones in very different lighting conditions.
