I have to completely disagree.
From WotC's own description... What is D&D?
"D&D is an imaginative, social experience that engages players in a rich fantasy world filled with larger-than-life heroes, deadly monsters, and diverse settings."
THIS is what D&D is. D&D isn't classes, it isn't THACO vs. d20, etc. Those are simply game engines or mechanics. Pretty much the only mechanic you can even truly call purely D&D is the use of the full polyhedron dice set.
(snip)
D&D needs to evolve, while keeping the core spirit of what D&D is... which is a social tabletop RPG. The physical mechanics do not necessarily the game make. New markets, new players are what will keep D&D alive. Does that leave grognards behind? Sure it does. Just like all the people who didn't want to give up LP's or 8-tracks. Sorry to them but they got left behind as life moved on. The same will and needs to happen with the RPG industry. Just because something "used to be" part of D&D (like Vancian magic), it doesn't mean it should remain a part of the game if there are other more progressive and better ways to handle mechanics.