2000 Cannondale Silk Road with "HeadShok" suspension
Perhaps inspired by earlier experiments with MTB-style RockShox forks, successfully used to combat the worst cobbles over the Paris-Roubaix race, Cannondale came up with their own twist by the late 1990s. An extra large diameter head tube on these bikes allowed room for single oil-damped shock absorber which could be locked out "on the fly" with a twist of the knob at the top of the threadless stem. With the stiff "bone-shaker" ride of Cannondale aluminum frames and equally unyielding carbon fiber road forks, anything would have been a welcome relief.
Carbon forks are often noted for their high speed vibration-damping properties. I always find them far TOO dead feeling. Since I don't ever hit high road racing speeds (such as 60+ mph on descents) the high speed vibration issues seem insignificant to me. On the other hand, at least in theory, the shock absorber makes some sense. For riding over rough city roads, the modest 15 mm. of travel could lessen an otherwise harsh ride... especially on these rough riding bikes.
...Of course, I can happily just stick with my Reynolds 531 steel fork blades, and slacker head tube and fork angles. If that's not enough... there is always room for a British "Roadster" type bike in my stable. 100 years of actual road testing over some of Great Britain's worst city and country roads, have shown those bikes can handle most any terrain with reasonable comfort and consistent stability.
Perhaps modern frameset materials have created problems which now require complex solutions to remedy... whereas earlier construction simply had no comparable "issues" to circumvent.