I can only speak for myself personally as anyone that knows me, I'm primarily an Atari collector as well as other precrash games and systems and for those of us who've been doing it for many many years, our collections are, for the most part, completed.

Also, as has been mentioned, when you become and old fart like me with a job, family, and other responsibilities, you don't have the time and inclination to go hunting all day for video games. I used to love it but the thrill of the hunt has kind of waned on me and if I do want something I buy it online (ebay is a last resort though).

But yes, there's a definite shift in collecting choices and the meaty part of the curve seems to be in the NES/SNES/N64/Genesis/PS1 era as opposed to my old favorites - 2600/7800/Atari-8bit/Colecovision/TandyCoco (ok that last one has a very small following) but I'm still very interested in the hobby as a whole and still visit Atariage daily and here (less frequently) to read and discuss everything retro gaming.

I think Atari will always be collectible but its just not the prominent focus for a majority of gaming collectors.