I agree with the OP's assertion that WoW is popular, and that some of the elements that make WoW popular should be explored for 4E. But some of the particulars I disagree with.
mxyzplk said:
Calm on down there.
1. Everyone has special abilities to use in combat.
This is one reason why WoW rules, and 4E is apparently integrating this reason.
2. Azeroth is a deep and interesting world.
Azeroth is okay, but no better than most other worlds. Also, WoW (at first) presents the depth of Azeroth very gradually, through missions, NPC text, items, and the vistas of Azeroth itself. The rest of the depth of the world is revealed at the gamer's choice of pace: the gamer has to seek out lore on websites and strat guides and whatnot.
This is similar to the way 4E seems to be. They present the bare minimum of info in the PHB--about the same amount of info that you'd see in WoW's chargen screens. Then the rest of the setting is revealed during play, by the DM.
I think 4E's approach to setting depth is therefore almost exactly like WoW's approach. It'd be a mistake to bog down the rulebooks with excessive fluff. And doing so would be a huge departure from the way WoW paces and presents setting info.
This comes down to DM and player style. Some groups see D&D as a series of combats that are loosely strung together by narrative. Some groups are more into the roleplaying, and combat is a rare event.
I guess the D&D equivalent of "instant action" is D&D Minis.
I recall reading something about early discussions of 4E, where the designers considered casting the DM in an adversarial role. I'm glad they went the other way. PvP is a terrible idea for a tabletop roleplaying game. It can be fun for a board game setting, or for one-shot sessions, but it should not be a major component of the core game.
5. WoW is easy. My 5 year old loves to run her dwarf around the newbie area.
Your 5 year old isn't playing WoW; she's clicking a mouse around and watching the actions on screen.

I'd call that equivalent to her picking up minis and moving them around a battlemat. That's not playing D&D.
But yeah, pace of information delivery and user interface are big reasons for WoW's success. D&D 4E should likewise be well-designed, well-written, and have excellent presentation. It should have a usable index, glossary, and elegant chapter structure. It should be printed on quality paper in a nice font with fantastic art.
As for ease of play, I think D&D 4E should definitely come with pre-gen characters and a pre-gen adventure. The rumored re-spec rules should help with ease of play. Same for the stated goals of making feat choices less critical to character effectiveness (the paradigm is that feats enhance abilities, as opposed to 3E's paradigm of feats providing abilities).
6. People can do what they want to.
Well, D&D (any edition) has WoW beat in this category. In WoW, I can't become king. I can't explore the ocean. I can't travel the planes, raze a town, build a cathedral. WoW is fundamentally limited to actions that the programmers have programmed. Sure, I can fish. But can I whittle?
WoW wins this one. The game has thousands of items. Each one looks cool, has different perks and abilities, and so on. Collecting ever-better loot is the crack that keeps people coming back for more.
I disagree that D&D should adopt the phat lewt system. I'm glad items are less important than they were in 3E. Characters should be heroes because of their inherent abilities and accomplishments, not because they've gotten lucky with monster drops.
But I do agree that loot should look cool. And a good DM will, when describing treasure, take time to make each item unique. That +2 Str boost item could be a pair of blacksmith's leather mittens, or fingerless cowhide gloves with studded knuckles of tarnished copper, or gleaming steel plate gauntlets, or strips of consecrated cloth wrapped around the hands, or whatever. I'm running a Savage Tide campaign on the Isle of Dread, and all the loot is tribal and primitive: the generic "Headband of Intellect +2" is a headdress made of brilliantly-colored Terror Bird feathers, the "Cloak of Resistance" is composed of Phanaton pelts, the "+1 Sword" is a stick with chunks of razor-sharp enchanted obsidian lodged all along the edges, and so on.
Point is: yes D&D can learn from other successful games, but it should absolutely not try to duplicate the WoW experience. They're both fantasy games, but they're played on fundamentally different platforms.