Good observation. The game is designed for you point and click where you want to shoot, not designed to destroy anything in the line of fire. The game play is a similar to Missile Command. If you shoot too far in front or behind the path of the object you will miss it.
I'll be adding additional weapons and one I've been considering is one that allows for everything in the path of the laser to be hit.
No physics engine used. All movement and interaction is calculated and drawn per frame using java-script and the Canvas Element