Okay, I'll admit it. I'm one of the people who downloads old games (NES, SNES, Genesis, C64, Arcade, etc), and plays them, while infrequently buying any new game. Why? I'm not willing to spend money on crap, and most new games, are, sadly enough, crap. Oh, and there is the issue of games never reaching the US. (Did you know, for example, that Tenchi Muyo was made into a game in Japan on the Super Famicom (SNES) platform? Some very nice fans have a Japanese->English patch out there).
So, having these games out there do decrease sales for everyone but Capcom (who will sell you a CD of their roms for a reasonable price, last time I checked. -- Never mind, just looked, they have bundled it with a joystick and is selling it for US$199.) *Sigh*
Does this mean I'll start buying new games now? No. I have my collection, and, although not complete, it includes most of the early eighty's arcade games. Plus, even if I manage to lose all of that, I still have nethack. The world's still good.