The 150kt speed refers to speed in the circuit and the reality is that while many GA aircraft CRUISE over 150kt, very, very few would do 150kt or more in the circuit. Most fast aircraft would be at IAP procedure speed or gear extension speed in the circuit and 120 kts is a common speed for this.
I'm not really sure who this applies to, maybe a Citation or something, but no GA single or light twin that I know of.