But you are missing part of the picture of our reaction system. A blink is a worst case scenario of seeing a threat approach our eye/face, the brain recognizing that threat after the image is processed, then the brain sending a signal to the musculature of the eyelid, and the eyelid finally completing the contraction. Our mind's ability to perceive a delay, or lag, in an expected response to touch is very different, because our visual center is already trained on the input and it's expected response before the action takes place. Seeing our finger touch something and waiting for the touched item to respond is simply a function of visual reaction time, which is very fast (as low as 10-20 ms). There is not a "decision loop" involved, or a brain to muscle signal delay, as with the blink. This lag perception is typically perceived by most humans once greater than 50ms. You can read volumes about this in articles about game and controller design, and even in TV's that have a "game mode" which reduces video processing to reduce lag in time from when player action is generated by player's console input to when the TV displays the action - such as sniping the perfect "head shot" in "Call of Duty", or in aircraft and simulator allowable latency times.
"Studies of Virtual Environments show that people are generally able to detect latencies as low as 10 to 20ms (Ellis, Mania, Adelstein, & Hill, 2004). Delay of 25ms did not have a measurable effect on the performance, but 69-75ms delay starts to show an effect (McKenzie, 1993; Jay, Hubbold, 2005). "
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So yes, absolutely, people can tell the difference in 50 or 100ms response time.
small screen innovation...Apple wants to make shore that all the iTunes purchases will be done faster then Google Play 
