I and the other photographers I know try to keep a pretty full range in the bag.
For me that's a 16-35, 28-70, 50 and a 70-200.
For pre-ceremony shots in the parlor, I usually use the 28-70 on one camera with a speedlight, and the 50 on the other camera. The 50 is a faster lens (F/1.4) and the depth of field it creates can really highlight the drama and romance of getting ready for the ceremony.
During the ceremony I usually use the 70-200 on a monopod. It's great for getting in close without disrupting the ceremony. But I also know people who use a shorter range like the 24-70.
For portraits after the wedding I usually use the 28-70 depending on how big the bridal party is. If I can swing it, I'll keep using the 70-200 since longer focal lengths tend to be more flattering. For light I usually have a speedlight or two (again, depending on how big the party is) on stands firing with the help of some pocketwizards.
During the reception I have the 28-70 on one camera and the 16-35 on the other. Usually both with a speedlight attached. The 28-70 does a better job when someone pulls you aside and asks you to catch a picture with so-and-so. The 16-35 is absolutely excellent on the dance floor.
I think the focal range mostly comes down to preference and personal technique. Most wedding photographers need zoom lenses because there isn't enough time be running back and forth to your bag to switch lenses. And, there isn't always the room to move around to compose the shot you want.
But, for the most part, just about all serious wedding photographers need fast lenses. F/2.8 or faster usually. Inevitably there will come a time when the venue for the ceremony doesn't allow for flash and in a dark chapel, f/5.6 just isn't going to cut it unless you boost the ISO up so high that all you can see is grain.
For any professional, I think it's wise to cover most common focal lengths. But even more importantly, to spend the money on good, fast lenses.