Micah, quite a few speaker manufacturers include two sets of speaker terminals, primarily as a concession to certain audiophile delusions regarding bi-wiring(aka "buy-wiring").
No, at a frequency where a speaker has an impedance of 4 ohms(the M80s are 8 ohm speakers over the majority of their frequency range)this isn't the result of two 8 ohm sections working in parallel to result in a net 4 ohms. As John B. pointed out, the effect of the crossover is to greatly increase the impedance of the section that's being rolled off. So, for example, at low frequencies the 4 ohm woofer might be operating in parallel with an upper frequency section which has an effective impedance around 100 ohms at those low frequencies. The net impedance in parallel would be around 3.9 ohms. At higher frequencies(if the impedance was 4 ohms, which isn't the case with the M80s)the effect of the crossover would be to raise the woofer impedance to maybe 100 ohms, which run in parallel with a 4 ohm high frequency section would again result in about a net 3.9 ohm impedance.
