Are grognards killing D&D? No, the strange market is.
To actually reply to the topic title -- specifically, are Grognards killing D&D, my opinion is, no.
If D&D is dying, and I'm not sure that it is (despite my and my gaming group's defection to FUDGE

), it's because of the very nature of the RPG industry itself. The publishers -- WOTC included -- are IMO in a cleft stick.
On the one hand, the only thing that sells are
systems. Typical RPG consumers don't buy adventures, campaign settings, campaign setting supplements, and similar products.
On the other hand, how many times can you revamp a system which does pretty much the same thing? And since the only books that sell significantly enough to pay the rent and keep the place running are
system books, the
only supplements which make economic sense to print are splatbooks that
expand the system. Yet at the same time, you can only add so many rules before the system becomes a cumbersome, confusing mess that disgusts the customer base, drives some of them away, and makes the others frustrated and suspicious when you finally sweep away the mess with a new edition (which then repeats the process).
In other words, the books whose printing would allow infinite fresh material without expanding on the original, streamlined system (campaign settings, adventures, etc.), while giving the company what it needs to continue on with, don't sell. So they're not made.
The RPG industry is sort of upside-down. There's an endless proliferation of system, and almost no material to use the system with -- precisely because people will buy so-called 'crunch' even if it's stifling the game, and eschew so-called 'fluff' even though it's what would allow the RPG industry to flourish
without making endless iterations of increasingly cumbersome systems.
To use a somewhat imprecise analogy, it's like people would buy DVD players but would NOT buy DVDs to play in them. In that case, you'd see all the companies coming out with revisions and add-ons for the players, and couldn't find a DVD anywhere, because there would be no money in them.
If people would buy 'fluff,' then a more-or less definitive ruleset would emerge, capping the amount of 'crunch' and removing the need for new editions. That way, they could concentrate on -- "here's our new, innovative, exciting game world where you can have fascinating adventures" -- instead of on "here's how we're handling Armor Class and non-combat skill synergies in version 388.45 of the bureaucratically maddening rules system."
I believe it's a fundamentally self-destructive business model forced on the companies by the upside-down buying habits of the people they have to sell to, who are fixated on 'crunch' and eschew 'fluff.' It remains to be seen how long they can keep the impossible juggling act going, that's all.
If anything kills D&D, in short, it'll be the customers losing patience with a flawed business model which their buying habits have imposed on those who make products for them.