I started working at Wizards of the Coast in 2000 as an advertising coordinator and it was soon after that Dungeons & Dragons: 3rd Edition was released. My impression is that D&D 3e was launched after a large playtest through fan gaming groups. I'm not sure whose brainchild it was to involve customers with the rules before they were finished. Was it Monte Cook, Jonathan Tweet, or Skip Williams? Perhaps it was Bill Slavicsek, Peter Adkison, or Ryan Dancey. I'll have to ask around.
4th edition rules was positively secretive. The 3rd edition of Dungeons & Dragons launched to much fanfare. TSR had really fallen apart and taken the D&D brand down with it. Game elements and marketing for 3e were designed to win the hearts and minds of existing players (though there was also a very expensive advertising campaign in mainstream magazines design to reach a new audience). You could "play a half-orc assassin" again and demons were back without the politically sensitive tana'ri label.
At least one blogger has speculated that part of the problem Wizards must overcome is us, the fans. Involving the disparate D&D factions in playtesting will certainly help each group feel a sense of ownership for D&D Next. This change from 4th edition's launch goes back to the method that was successfully used in 2000 to win back customers disaffected by TSR. If the only problem had been that D&D 4e was forced onto fans then I don't think we'd be working on 5th edition already.
Had the fundamental game of 4th edition been as robust as 3rd edition, enough players would have converted to make it a viable business. Instead, 4e has moved in the opposite direction. Players who gave the new edition their full attention eventually abandoned it because it was imploding. What 4th edition desperately needed was a lot more playtesting. In testing it's key to repeatedly engage with an element with minor variations. The number of game mechanic interactions that get encountered and tested increases exponentially as you expand the number of groups playing the rules. Insufficient testing is a common problem in software. Computer games are so prone to this problem that new releases can include a Beta period where the mass of potential customers is searching for code bugs for fun. No matter how much insider testing goes on, it can't reach even a fraction of the bugs that will be discovered once the game is "in the wild" being played by masses of customers.
I'm thrilled about D&D Next's approach to playtesting. I'm not excited because of the opportunity for fans to design 5th edition, rather, I'm excited to know that the game designers will have good data upon which to base their decisions when structuring a rules engine that will last.