In my opinion, the King is dead, long live the King. I've talked to several 4e players in my area, and most of them love the system but admit that they aren't having alot of fun because the published adventures are weak or the DM running the game isn't as skilled as the one who stayed with some other system. This will ultimately kill WotC if they don't do something about it. They IMO have to hire top quality talent to write their adventures. Reading a 4e adventure compared to what Paizo has put out reads like comparing a kid's work to mature designer. I'd buy 4e adventures solely to convert them if the story was good enough.
Seriously, it has always been my opinion that the #1 reason for the success of D&D relative to other RPG product lines was modules. As a guy who runs games, I love to see a small core line of rule books and a shelf brimming with adventures. That's the system for me. In my opinion, quality GM aids are the determining factor in the success of your RPG. If you turn out good adventures, people will play your game, and simply no other RPG product line has had over the years the focus on adventures that D&D has. What it means is that more players are willing to become GM's, more adventures get actually run, and you end up with more fans.
I once read someone reviewing the rules to Chill and wondering why the game retained a small but enduring fanbase. The answer is simple - adventures. What's the most awesome sauce thing about Chaosium CoC - great adventure support. If you don't have great adventure support for your system, ultimately you just have a GM toy and you sell books to be read by DMs and then put on the shelf never to be actually used. I've got several of these. Heck, the majority of the GURPS product line as best as I can tell qualifies. Sure, a few GMs will be inspired enough to run a game or even a campaign, but some will suck, some won't want to put in the continued work, and with the small group remaining you never grow your market.
I don't care whether you think Pathfinder sucks and 4e is the system bomb or vica versa, if you want to look at what system is going to succeed over the long run, look for which one is putting out the strongest adventures. If they are both putting out strong modules, then they'll both succeed. But if one falters in that, then you can bet the other one is where all the players will end up in the long run.
Even if modules didn't sell, they are so important to the RPG business model that you'd want to sell them at a loss IMO. Having a great system but no modules is like having a great console, but no video games that will run on the system and expecting to have a huge market because people will want to write their own video games. You have to have video games to sell a video gaming console. Of course, Paizo appears to have realized that you can make money selling the games as well, and in fact, if you do it right, you might can make more money on the games than on the 'console'.
Good points. But I do think WOTC is mostly concentrating on crunch as their focus (their constant errata is also an indication) rather than fluff material. If you look back a AD&D, though the game system many would consider clunky, alot have fond memories of it's adventures and are still being talked about until this day. Heck the good ones are being revamped (Castle Greyhawk, Ravenloft, ToH) back in 3e and now 4e.
I think many 4e players are using the rules to run their own adventures or Paizo's adventures. There is even an outcry of wanting Paizo to make adventures for 4e, and that says alot.