It should also be noted that the complaint that the OSR isn’t innovative enough is somewhat missing the point of what the OSR is. Of course the OSR doesn’t go off in bold new directions, exploring the bleeding edge of game design! It’s not supposed to, at least not on a grand scale. By definition, the OSR is a deliberate harkening back to earlier forms, attempting to get new and exciting modes of play out of them. People who are looking for deliberately (I might even go so far as to say self-consciously) new and innovative systems and settings should be looking at Indie Press Revolution and the like. The OSR is what it is, and condemning it for not being what it isn’t, doesn’t make a lot of sense.
That is not to say that the OSR doesn’t innovate; quite the contrary. But its innovation is, for the most part, contained within the boundaries of the older forms. It is variation (sometimes inspired) and expansion (ditto), but it is not plunging into unexplored territory. If it was, it would be something else. And remember, that is not a Bad Thing! Castles & Crusades is a prime example of this; most of the outlines and fundamentals of AD&D are there, but the d20 universal mechanic is an innovation within those broad outlines. Change it too much, though, and it moves outside of the comfort zone.
This is an important facet of marketing the OSR because it speaks to one of its fundamental strengths; familiarity. For a segment of the target audience (not by any means the whole of it, as will be mentioned in the next installment), the fact that a game is so much like a previous edition is a selling point in and of itself. It's not necessarily a question of nostalgia (although that's certainly a part of it for some people); if it were, then the "movement" would begin and end with people buying the original rulebooks on eBay or breaking them out of the attic, playing for a bit to recover their lost youth, and fading off again.
What the retro-clones have to offer that segment is familiarity. If I know that I like the broad outlines of how the AD&D game system is built-- classes, Vancian magic, saving throws, fairly abstract combat, etc.-- then I can be pretty sure that a game that is close to AD&D will be something I'll be comfortable with, even if some of the particulars are different. This connects with compatibility; if a product is compatible with a game I already know I like, I'll be more inclined to buy it, because I know at least the basics will be familiar.