High speed video of an LCD refresh occuring in real-time:
Also, input lag is the whole chain, INCLUDING how long it takes to display.
See AnandTech's article:
CRT's are only zero input lag at the top edge of the screen.
CRT's even have input lag for the bottom edge of the screen, because they have a finite frame transmission time (scanning from top to bottom).
Some gaming LCD's (certain BENQ and ASUS gaming LCD's) are the same way; they scan the pixels top to bottom in real time too (as seen in high speed video).
We're talking about input lag from game engine to human eyeballs, so it WILL also include frame transmission time (From computer to display), including any display mechanisms (scanout). nVidia G-Sync solves the problem by using ultrafast frame transmission times (1/144sec, even when running at 60Hz, since G-Sync uses a dotclock for frame transmission/scanout times of 1/144sec) -- they clearly explained it in their video.
Now, strobing does add a minor input lag, but an average of less than one frame. (For LCD's with less motion blur than CRT"s, google "lightboost" -- John Carmack said he uses a LightBoost monitor)