VGChartz is a site for tracking and discussing video game sales, is not? This topic is a video game sales discussion. So, I think it's relevant, regardless of what year or generation the topic pertains to.
True, but arguments about over/ undertracking come up all the time, and VGC only ever makes changes when there is official word from the corporations themselves. PS1 did amazing. Regardless of whether it's off by 1.5 million or not. Besides, this was probably brought up already, and VGC has had almost a decade to do their research and fix it if it was wrong.