In the second example, the speakers are wired together in parallel; there are two paths for current to flow. If the speakers are the same impedance, then each will flow the same amount of current, for twice the total amount that the single speaker would otherwise flow (for a given voltage). Therefore, if each speaker is 8O, the overall circuit impedance is 4O. It should stand to reason that a single 4O speaker would flow the same amount of current.
Audio amplifiers are designed to drive a specific speaker load, usually 6O to 8O for most modern home audio receivers. The percent Total Harmonic Distortion is generally lower in an amplifier driving an 8O load, even if designed to drive a 4O speaker load. Most home audio speakers produced today are rated at 8O impedance.
As you can see in the wiring examples above, how multiple speakers are connected to an amplifier channel has a great affect on the performance of the amplifier. If not rated for a 4O load, an amplifier connected to such a load can over heat and shut down, or possibly even be damaged. Also, an amplifier will not provide its best sonic quality driving an impedance load heavier than it is rated for.