Scaling in Object Mode, means you are Scaling the Coordinate System of that Object (whether it’s a Mesh or a Curve).
If you look at this picture, the Handles of the Control Points of the left Curve (Scaled in Object Mode) are about 1.1m apart, while those of the right Curve (Scaled in Edit Mode) are about 2.2m apart. When you Apply the Scale, the distance between the Handles of the left Curve doubles. In 1 Axis (the Tangent), the Size of the Control Point changes.
This doesn’t explain completely, what is happening, but it might give you a gut-feeling, why the behavior is different for Curves, than for Meshes and keep you from diving into the rabbit hole (it’s not worth it, believe me).
