The connections have virtually no resistance but if they did that would add even more resistance, not subtract it. I'm pretty sure the impedance seen by the amplifier is 1 ohm, not 0.5 ohms as stated by the diagram.
ETA: After looking at the diagram again, now I get it. Each speaker has 2 4-ohm impedances in parallel. So it's really 8 4-ohm resistors in parallel, which is 0.5 ohms.