I heard this argument a hundred times:
Let's tell you a story. I was running a session once, three experienced players and one newcomer.
The session was supposed to be a difficult detective story about someone murdering Cormyr Ambassador in Waterdeep. Several suspects, three different factions, a lot of personal working and a lot of dangers. After 15 minutes of story the newcomer said "F*** this, let's roll gather information and whang the bad guy".
It doesn't matter on what you can do with DnD. The fact is that WotC killed or abandoned all interesting, hard, and playable settings (Planescape, Ravenloft, Darksun, Spelljammer), and choose to develop soaplike regular fantasy like Greyhawk and Fearun. Most of source books feel like buying a booster for a card game, you get a lot of new spells, feats, prestige classes, a lot of new numbers, and little of anything else.
Lastly, during 14 years of running and playing RPG I've met a lot of players. While almost every one of them was playing DnD at some of point I've found one regularity. All role players moved to World of Darkness, Warhammer, Riddle of Steel or similar, less concerned with mechanics, more with story and character development systems. All Roll players talk about their +5 maces of Mood players smiting, and make jokes about role players while they loot dragon treasures.
I still enjoy playing Dungeon and Dragons miniatures, and I still play and run regular DnD. But just as a simple fantasy, when I'm not in a mood of another session of 200 years old Vampiric intrigues, and in the mood of bringing my Temple Rider of Olimadara for another adventure.
DnD for me is something of a like of an simpler, more board game like type of an RPG experience.