Ok, I went and did some research:
1. Mario Bros 3 (not really a precision platform, but anyway..)
- acceleration/deceleration
- inertia in air is maintained when you let go of the button
2. Super Meat Boy
- very small acceleration, immediate stop on ground when you stop pressing the button
- inertia in air is also maintained
3. Celeste
- seemingly no acceleration or deceleration
- inertia in air stops when you let go of the button
I was actually a bit surprised to see that was the case in Celeste. So it seems like the answer is: SOMETIMES :P follow your heart! I still think gravity should be reduced ;)