I think the difficulty arises in that most movement (swimming, flying, climbing, etc.) requires significant activity (50% or more, which precludes making an attack). The exception is walking/running, which can be performed in small increments (e.g., 10% for bookkeeping ease).
So, let me throw out an interpretation:
* A moving maneuver requires at least 50% activity.
* In some cases (such as climbing or swimming) you can choose not to use all available movement (or even choose not to move).
* In other cases (such as skiing or flying) you must use at least 50% of the available movement (i.e., stopping is hard (skiing) or impossible (flying)).
* Walking/jogging/running is (usually) not a moving maneuver (it just takes activity), but sprinting (and faster) is a moving maneuver.
* One can allocate up to 40% to movement (walking/jogging/running) and still make an attack at a penalty.
* While making moving maneuvers, one can make a "Moving Strike," in which case the difficulty penalties apply, and can be offset by Moving Strike skill.
The major drawback is dealing with an opponent that is running away (i.e., both participants are moving at a run pace).
The charge modifiers could be applied in either case, or just in the case of a sprint+ attack.