@Rahul The dude does have a point. The problem is he seems to have missed the two decades of time where the definition of the phrase evolved to include more than stuff blueprinted on D&D.
Interestingly enough though, D&D has evolved with this definition. More emphasis is being put on premade campaigns with premade characters (backgrounds, items, stats, etc.) in premade dungeons completing premade quests than before. These games often take place at cons or other special events. I've even played a few with friends in private who were designing some to run at cons.
Does the purity level drop? Sure. Does that matter? It shouldn't if the games being made are of quality. Newsflash to Daniel Erickson: They are.
@Nels I dunno, I think definitions should have an agreed-upon meaning otherwise what's the point. FFXIII isn't an RPG considering that it throws most of what defines even a Final Fantasy-esque RPG out the window. I'd say 13 is more reminiscent of MGS4 - they threw out a lot of series conventions there too, and ended up with something that didn't feel like it belonged anywhere. The creators can strut and talk about how "we made something that can't even be considered an RPG anymore" but I'm not sure that's a compliment in these cases.