John,
That was a very lucid treatment on amps and ohms, the only addition I'd make is that some modern amps 'do' account for speaker impedance dynamically. For instance, NAD's Powerdrive circuitry. Instead of me explaining, I'll clip some text from the data sheet:
NAD's PowerDrive™ technology measures load impedance continuously on each channel and adjusts the power supply voltage for maximum undistorted dynamic power into the connected speaker at all times and under all operating conditions. The signal processor also continuously measures temperature and average long term power and, based on this information, chooses the optimum voltage.
