I honestly don't know what the differences between the units is but oHms law doesn't lie! It could be 2 different units from 2 different era's (PIONEER IS known to re-use the same model #'s over and over!).
Differences in Amplifier class (A,AB1,AB2, C, D, G, etc) will draw different amounts of current at maximum load and output the same amount of watts. Class A, AB1, AB2 IIRC are the biggest current hogs. Class G or H is the least from my understanding. Not withstanding transformer differences, you have to look at the topology of the amp.
Also the different Governmental bodies that determine standards are ALL DIFFERENT. A GOOD EXAMPLE is the SX-1080. For the same unit (from the manual).
POWER REQUIREMENTS.......................120V, 60Hz
POWER CONSUMPTION.........................350W(UL), 800W(CSA), 1100W(MAX).
The SX-1080 was produced at the same time the SA-708/SA-7800 (late 70's), and it looks as if as time went on PIONEER added more and more specs to the manuals to satisfy the gov't bodies.
As for your examples (Pictures). The 220/240 unit is definately European MARKET. The 4 voltage unit is most likely a universal unit that would satisfy most markets. I don't know how they determined the wattage, but it's there.
As the Voltage drops the Watts Stay the Same, based on ohms law, and the calculations in my 1st post. It's still consuming 200W, but at 240V that is .833333333~ amps, and at 110V is 1.8181818181~ amps.
As for the 600W model, it may be identical to the 190w model (other than the transformer voltages), but the gov't testing is different. Load is determined by the circuits internally, not the transformer. The transformer is mainly a supplier, not a user except for a slight amount.
It's one of those mysteries that is probably lost in some beaurocrats file's in a large gov't warehouse never destined to see the light of day again.