This thread really needs to be retitled. SO let me say this in bold...
THE SUBS ARE NOT WIRED INCORRECTLY.
The way the subs are hooked up is entirely correct by all rules of wiring and circuitry. Your multimeter will read no differently regardless of how you connect it. It may even read no resistance because a speaker is what is called an "inductive" load. It has a resistance to AC current, but little or none to DC.
The way the system is installed in our cars, however, the system is not tuned. What does this mean? This means that the bass from your front speakers stands to cancel out or interfere with the bass from your subwoofers. See the
Interference article at Wikipedia for the explanation on wave interference.
Rewiring the subs as the OP has suggested inverts the phase of the subwoofers. To get technical, it shifts it by 180 degrees. This changes the way in which it interacts with the front speakers and, as it so happens in this car, it seems to result in an improvement.
Mind, it still won't be perfect. The only way to get it perfect is to get a specific EQ or tuning box, run ALL of the channels through that, and specifically adjust the delays at each speaker so that the waveform from each hits your listening space at the exact same time.