Let me take on the devil's advocate role for a second (in fact, just half of one). The problem of preserving video games for the future is of course an important issue (and of electronic media as a whole; how in the world will anyone know what we were doing on the Internet, or if we ever had it, once it's been put to pasture a hundred years from now?) However, let's be a bit practical here; if you see someone playing on a DS or Wii emulator, they're not doing it to experience ancient artifacts from an era long gone.
I won't make assumptions on what people may or may not be using emulators for, but I will note that as of right now, The PS3, Xbox 360 and Wii aren't the only consoles still being actively played with. If you look hard enough, you can actually find PS2s and GBAs still whirring into action, executing its original purpose. Yet even those people that may be able to access these not-so-rare pieces of hardware and accompanying games may still opt to use emulators and soft copies floating on the net. These people are likely not focused on experiencing history; they're circumventing legitimate existing avenues for convenience.
Let's go further back, though, to the time of the PS1 and Sega Dreamcast, or of the 8-bit and 16-bit era where many other platforms still existed. It would be highly impractical to attempt to gain access to the hardware and software of the day, even more so through traditional means. You might get lucky with the occasional collector who can sell you a unit for a ridiculous sum, or a pristine copy of Crash Bandicoot 1 for even higher, but not everyone who would be willing to pay that much could find such sellers. For these people, the context shifts dramatically because emulation becomes the only practical option.
There's a case to be made for the timing of when emulators pop up. If units of a given console or game are still in circulation, the consensus seems to be that the people using them tend to do so because they don't want to invest in said product. If, however, a certain amount of time has passed and the original product is no longer procurable through any other way than emulation and soft copies, it becomes much more understandable and less shameful (though still pretty nerdy;)) to proclaim actively engaging in game emulation.
I ultimate point is: emulation is not bad by itself, but only under the right circumstances and context should it be practiced. I would love for a major console maker to make an announcement that they will open source the hardware and API implementations of way-past EOL consoles (Atari, Amiga, even the NES) as a display of support for the preservation of our history and culture that is video games.