Savvage of Spinebreaker quickly responded that big guilds have their place, but "People can now play in closer more tightly-knit groups..." For many players, raiding offers sufficient challenge while being more enjoyable than it once was. The raiding experience is not only more accessible, but also more fun. Smaller guilds can afford to be more selective of the online personalities of their membership, while still being able to to make progress.
That being said, there are still many people who are not willing to put time and effort into raiding. They seem to want to have epics handed to them, without going through the proper progression. I've seen many come into raids completely unprepared. They don't study the fights, but instead believe that they can "tank and spank" their way through anything. This simply isn't the case with most raid bosses. Raids still require adequate preparation. Just because you can get in the door does not mean you're ready to roll.
Blizzard has also added content for those seeking more of a challenge. Awyer of Cho'Gall noted that very few guilds have "hard mode" achievements under their belts. For some, WoW may be "World of Borecraft" as the OP puts it, but there are still opportunities for the top guilds to build and excel. WoW will always have its rock stars, but you don't need to be one to enjoy the endgame content. I believe this is as the developers wanted it, and thus it is so.
There are still guilds out there with massive rosters. There are still guilds out there pushing the edge of content. There are just many more smaller guilds that have an endgame presence.
As a side note to Sternbridge of Blood Furnace. If you want to move away from keyboard turning, it just takes a little bit of reflex training. Get a feel for moving with your mouse. Run through cities and buildings until you are comfortable with it. Then go into an easy area, maybe somewhere in Outland and bind your keys. Give it an hour or so. Even if it's a little frustrating at first it'll soon be easy and natural.