There will be a different reason from every single person who gets onto the preservation path, be it preserving magazines of any kind, or games for old computers like Atari's & Amiga's etc. Even old school comics of yesteryear.
However, when you step back and look at it objectively there tends to be one all-encompassing reason for doing it. That is so future generations ... our children & their children can see where it all started & how the people of the past like us viewed viewed the events of the day. I am not talking about the people blatantly pirating current materials and causing no end of financial hardship for those trying to make a living releasing current products, but those of us who look at a 20 year old object and realise that the publishers may have long disappeared and that it would be a tragedy & an insult to the people who created those wonderful works if they disappeared forever.
Interestingly, as time goes on it is not only becoming increasingly easier to preserve old works due to technology, but there is more awareness of the fact that people ARE interested in seeing or using them.
Emulation of consoles and PC's of yesteryear through increases in todays PC processor power have seen emulation become as mainstream as the Xbox 360 or PS3 gaming of today, to the point where the manufacturers are sitting up and taking notice. Your example of the Wii's virtual console is a prime example where a company has seen the fact that emulation is pervasive & where old products can once again become a revenue stream from a new generation of users.
Playboy is another example where the underground preservation of their older magazines has made them realise they are still highly popular and they are now releasing DVD compilations of decades old products for the digital age. And more power to them for doing it.
So I'll end this with the reason I scan old gaming magazines. It would an abomination if in a hundred years time someone can read a Playboy of today, or play an emulated game of Space Invaders or Gauntlet on thier Xbox 9500 but when asked who made the game or how the Amiga came to be no-one can say because the old literature of the day hasn't been preserved. THAT's why people like myself do this.