Fascinating discussion here, but I think a lot of people are taking for granted that the mere existence of the DDI, specifically the Character Builder (CB), somehow locks all third-party publishers out of the "crunch creation for players" game.
I don't think that is true, at all. The CB is a fantastic tool; but it just that, a tool. As Obryn has said several times, if you make a good enough setting, with good enough player-crunch tied to compelling fluff, then you can surely convince the players to put up with the minor inconvenience of not being able to use the CB with your product. (At least, not out of the box; of course you can add custom elements yourself.)
As an aside, my anecdotal evidence* seems to indicate that the use of the CB is far from 100% among the 4e players I know. Some players don't want to pay for the DDI; some players don't like the DDI or CB for whatever reason; some players just prefer an alternate "output" -- so while they might use the CB, they don't print out the power cards or character sheets; they write things by hand. And if you're going to write things by hand, then using third-party stuff is no big deal.
* Yes, I'm well aware of the dangers of anecdotal evidence, and I frequently rail against it, but it's all I've got. Heh.
One thing I do agree with, that has been said by various people in this thread, is that these days you cannot simply churn out some barely competent third-party product and expect it to sell. First, you have to compete with the seemingly newly invigorated Wizards of the Coast, which has the might of being official, the economies of scale, and top-notch production values.
Second, you have to compete with the other third-party companies that are veterans of publishing for D&D (since the 3e days), and many of which have production values on par with WotC's.
So if you want to launch a product these days, and you expect it to be a "big success" (whatever that means), you'd better bring your A game. And I for one am eager to see people do this, because more competition, more new products, more new ideas, makes the game better and more entertaining for everyone.