DISCLAIMER: This post makes a number of unfounded assertions based on my understanding of how the RPG market works. If I'm wrong, just remember that I am a delicate snowflake and you need to be gentle.
Another thing: you need a lot of books, but you HAVE to do with without bloat, and it has to still be quality. At my local B&N the Paizo books outnumber the D&D books 3:1, simply because of the sheer number of titles. And these are NOT "advanced" books or somesuch with rules bloat. For the most part these are adventures, GM helpers like the NPC Codex, etc., i.e. things that help GM's start and run a Pathfinder game. Meanwhile, the 4E books are all player options books. Players don't drive your sales, DM's do.
I think the heart of it is this: stop making books for players and start making books for GM's. Adventures, adventures, adventures. Stop putting them on the website and start putting them in binding and battle Paizo for shelf-space. Don't make adventures this add-on afterthought to selling the core rules. Rather, make the core rules just a gateway into the purchase of adventures and modules.
NOTE: I don't buy adventures or modules. I have no care for them at all. As a player, I buy every player options book I can get my hands on. But the fact remains that I am in the vast minority (I think), and I am not one to be catered to. Ever. I'm niche at best.