Some spikes are more cone shaped than others. Cones run one way when it comes to vibration. They 'drain' vibration from the speaker cabinet and dont permit vibration from traveling up from the floor. Thats why with cones under components and stands you get less vibration.
As for speakers moving, I have seen speakers and subs "walk". Its the vibration of the cabinet that you are trying to reduce. A drivers motion will be more precise if its 'working against' a solid stationary baffle to start and stop from , as opposed to a vibrating baffle. Spikes ususally improve the sound by giving the drivers a less resonant platform so they work better and also by reducing the sound you may hear from the cabinet itself.
As for speakers moving, I have seen speakers and subs "walk". Its the vibration of the cabinet that you are trying to reduce. A drivers motion will be more precise if its 'working against' a solid stationary baffle to start and stop from , as opposed to a vibrating baffle. Spikes ususally improve the sound by giving the drivers a less resonant platform so they work better and also by reducing the sound you may hear from the cabinet itself.