The logic behind it is that if you're traveling at higher speeds, more granular differences are rather unnecessary and it leaves more needle travel for the more common speeds where you would appreciate knowing you're doing 43 or 27, for instance. It's actually easier to implement on a digital gauge than on an analog one when you remember in analog you would have to make the speedometer needle switch between at at least two different speeds. seamlessly, at that.
Saab used to do something quite similar in their clusters, This is apparently a Saab 9-5