I'm somewhat sad that diversity is seen as a bad thing by many people involved in this hobby. The OP here, for example, appears to envision the hobby as a single game and views any deviation from that One True Way as inherently detrimental behavior.
I've been buying RPGs etc since 1981 or so. Diversity was something to be celebrated back then. I'm a little annoyed by the perception that homogenized rules are more important than diversity. Fans of the OGL proclaim that it's beneficial because it's supports D&D and it's good for WoTC, but for about 20 years or so, the hobby had people who could play D&D, CoC, GURPS, Storyteller, Runequest, RIFTS, and Traveller, to name some of the more popular games, and nobody ever seemed to think "jeez, shouldn't there be one ruleset"?
I think the hobby is actually less healthy since there was so much d20/OGL stuff and a glut similar to what TSR did to themselves in the mid 1990s affected the hobby. While there's a lot of "d20-based" product out there, a lot of the more experimental stuff has left and I think that more than anything hurt some of the other game camps.
D&D dividing into sub-camps is likely inevitable. The game has made several extreme changes, with now 3 rule-bases: 1/2 Ed AD&D (both are pretty similar so I count them as 1), 3rd Edition D&D, and now 4e. Doing this is always risky and you give up the loyal fans for new players by doing this--the key is to minimize its effect. I'm not sure by deciding to change their settings and rules so radically this time out they are doing as much to keep the fans as loyal.
The OGL has also given a lot of creative folks the ability to write their own spin on D&D. You'll note a lot of people who used to work for Wizards and TSR left and freelanced or formed their own companies. If they wanted to avoid that, WoTC should have not created an OGL and should have worked to keep the freelancers on staff or with exclusive contracts.
Is the hobby healthy? Well, it's lost some players to computer games, and will likely become a little more of a niche hobby like tabletop wargames?
Is D&D healthy--hard to say? I think eventually it will fall down as the #1 game. I think the fracturing will happen. If Hasbro suddenly pulled the plug on D&D support and didn't license out 4e, you'd have maybe 4-12 players all doing OGL-styled games based on 3e. Because there is no company with the trademark, the D&D player base naturally splinters, and I think a player like White Wolf, Games Workshop, or somebody of that size would end up having the #1 game.
Life is a series of evolutions and revolutions. We can't expect our favorite thing to last forever, or at least always be popular and #1.