Not to be pedantic, but letterforms are fundamentally chain-able icons and those have been around since written language.
More contemporarily, other marks/icons we now would think of as standard are really icons for language control or words themselves. Typographers have been using monochromatic marks and glyphs since the dawn of the printing press.
Typographical symbols work in part because they exist within a specific problem domain whose practitioners are trained to understand them, and also because the constraints of their native domain privilege function (expressing some directive regarding how a given chunk of text should be typeset) over form (the look and feel of the glyphs themselves). Neither of these properties seems likely to be guaranteed for the much more general domain in which web icons exist.
But the types of icons were talking about here (clock, fork and knife, location marker, star, etc.) do not have such a long history in web design as being monochromatic. It's a fairly recent design trend. A fork and knife icon (used to represent restaurants) could just as easily be a detailed, shaded, multi-colored icon.
More contemporarily, other marks/icons we now would think of as standard are really icons for language control or words themselves. Typographers have been using monochromatic marks and glyphs since the dawn of the printing press.
So, not a flash in the pan.