It has long been known that flicker can reduce motion blur. It is why CRT displays still have less motion blur than most LCD displays.
Some 120Hz monitors have a strobe backlight that eliminate motion blur.
Motion blur reducing strobe backlights (e.g. LightBoost) puts black periods between frames, and is more efficient than this software-based black frame insertion.
The motion blur you see is caused by eye-tracking (sample-and-hold), see related TestUFO: Eye Tracking Motion Blur Demo.
Some emulators (MAME, WinUAE) use this technique for 60 fps on 120 Hz monitors. See www.blurbusters.com/mame
For most LCD, the half framerate animation creates a 50%-50% duty cycle of flicker, which reduces motion blur by approximately 50% on most LCD's.
For CRT and LightBoost, this animation is more dramatic, since it eliminates the double-image effect (30fps@60Hz with the clarity of 60fps@60Hz).
Also, this animation flickers more on 60Hz monitors (bad 30Hz flicker), while it looks much better on 120Hz monitors (better 60Hz flicker).
WARNING: This animation should not be viewed by persons susceptible to epilepsy.