I believe the classic console information is pretty accurate, because it wouldn't take too long to read through alot of old hardware information from the major companies (Atari, Sega, ect), as they publish quarterly hardware shipping information.
The issue is when it comes to current systems like the 360, Wii, PS3, et all, as we're trying to get up-to-the-minute information, which isn't quite accurate all the time.
Back from the dead, I'm afraid.