Yep, "Responsiveness" is all about how FAST the Fuel/Air can get into the cylinder, after you stomped the gas.

Smaller carbs(and smaller intakes) maintain a slightly higher pressure drop than a larger one. More pressure difference between the inside of the cylinder and the ambient(outside the carb), the HIGHER the air(fuel too) Velocity will be.

Higher air velocity at lower speeds = more "Responsiveness"

Small cams and more indirectly small tube headers, help maintain this higer Air/Fuel velocity at lower RPMs.