There is the belief that "no new products" = "dead game" = difficulty in getting new people to play it. So then, "new products" = "living system" = grow the player base... just by virtue of new products existing.
I know that belief is out there, but considering the huge number of products for D&D and AD&D available at very low cost in PDF format, I'm not sure that just having new adventures for these older systems is going to bring in many new players. I think Labyrinth Lord is an example of a more effective way: a retro-clone game that is a complete "new game" package. Yes, its primary purpose it to allow people to publish adventures "for Labyrinth Lord" that are compatible with B/X D&D. However, it was packaged as a complete new game with a catchy title. I can see someone seeing Labyrinth Lord in a shop and deciding to give it a try. I can't see that as very likely with OSRIC (at least the first edition. What might help even more is a retro-clone game with an edition aimed at new players with art and layout more like current games.
I don't think it's that easy... but it certainly doesn't hurt.
You're right. It definitely can't hurt.