Yes i never considered this much but as far as i can remember NEC didn’t mention voltage rating as a condition to permit the absence of a motor disconnect.
I do not have my NEC book but i do recall that under some situations that in order for the branch circuit breaker to serve as the motor disconnect it would have to be within sight or 50’ from the motor. Perhaps due to the 1/8 low hp this doesn’t apply here?
This post brings up a good point because many outdoor motors can be beyond 50’ from the breaker panel. So a disconnect would be needed
Also i would like to point out that one disconnect can serve multiple motors if its sized to code and proper horsepower rating
I can't remember what year they changed the rule a bit, maybe 2005 give or take a code cycle or two. But you used to be able to use the disconnect for the controller as the disconnect for the motor when not within sight of the motor if that disconnect had locking provisions. This was used a lot in situations with MCC's because your MCC bucket had a lockable disconnect and of course is the controller disconnect as well.
Now that is mostly only an allowance for some the situations that have been mentioned here and the general rules do require a disconnect at the motor.
1/8 hp or less has and still allows the branch circuit device to be the motor disconnect. I don't know how they came up with 1/8 HP. A 1/8 HP motor that is running can certainly have enough mechanical power to be harmful, though many maybe wouldn't have enough starting torque to be too much of a threat if they were to attempt to start while working on the motor or driven load? Electrical shock hazard certainly doesn't change with HP.
Never really been any voltage limitations that applied in any way either.