The idea behind that was to allow adjustment of the in/out points after they are set, sort of for fine-tuning the marks. But you're right, it's probably better to keep all the controls consistent; do you think clicking and dragging the playback slider with the mouse should also obey the in/out points?
I would think the only mode that would allow you to go past the mark points would be the playback slider, since it is visually showing you that there may be frames beyond those points. Otherwise, normal playback and jog playback should obey the mark points. At least that's my two centavos worth!