The example uses an adjustable "threshold" to set the sensitivity of the sensor. In the example the threshold is set to 550 which is approximately Vcc * 0.5.
Using a digital input means that there are two thresholds (Google "hysteresis") and they are fixed. Any voltage below Vcc * 0.3 is LOW, any voltage above Vcc * 0.6 is HIGH. What the input reads in between 0.3Vcc and 0.6Vcc depends on the last state. For example if the input was LOW and rose to 0.45Vcc it will remain LOW.
So like PaulRB said, it depends on if the sensor output will be high enough to register a HIGH and low enough to register a LOW.