There have been a few very interesting posts in the old-school blogosphere recently, most notably one from Mr. Raggi over at LotFP, and one from Mr. Shook at LotGDs, each in their own way trying to balance the various "D&D" rule sets out there with the current momentum of the "Old School Renaissance". Good reading.
I'm perhaps a bad person to discuss this topic, as I feel books like "A Princess of Mars", "The Swords of Lankhmar" and "The Black Company" are far more important to your gaming experience than whether you choose between OSRIC, Labyrinth Lord, or D&D4E.
That said, I think one of the biggest reasons gamers are flocking (can I say "flocking" here?) back to the older editions specifically (and their modern simulacra) is that these rule sets are simpler, and thus more easily adapted to fit what each DM/group envision as their ideal game world. It's easy to say that OD&D and such were too amorphous and ever-changing to qualify as a flag for the old-school movement to rally around, but this is only valid if you were around at the beginning to experience it.
A large number of gamers I know picked up the hobby during the AD&D 1E days, left after 2E came out, and came back to it after 3E through a mixture of curiousity and nostalgia. While 3E, and even 4E, can be enjoyable under the right circumstances, they certainly aren't going to inspire the legendary gaming experiences my 30-and-40-something generation remembers fondly from their youth, nor recreate the gaming exploits they read about greedily in old issues of Dragon or witnessed as teens at conventions with veterans-at-play.
What simulacra like S&W and LL do exceedingly well is give modern gamers easy access to concise, inspired representations of the oldest editions of D&D, and lets them develope their home games naturally from there.
As OD&D gradually morphed into 1E AD&D and B/X in the late seventies, fell into corporate hands in the late 80's and gradually morphed from there into the rules-heavy 3E (well, what did you expect with a Rolemaster vet as a lead designer?;-), so can LL, S&W, and OSRIC morph into something altogether new over time. Only this time, it could do so in the hands of the old-school gaming community, with no corporate interests in mind.
Whether these disparate editions will morph into a unifying old-school edition to rule them all, the lack of which Mr. Raggi laments, remains to be seen. But I do think some evolution is inevitable, and given the current climate of creativity and respect for D&D's roots, most likely headed in the right direction.