The test is indeed dubious. However, what would you use to explain IR drop to an unscientific person who needs advice?
Their test does that, in an most "illuminating" fashion.
We all concur that larger guages drop less, many of us can detail that from simple calculations, some from the atomic level. But overwhelming the consumer in this way doesn't make a sale, all it does is produce the "deer in the headlight" reaction. Monster's display does accurately depict powerloss to the average consumer.
Cheers, John