I'll be honest here. I'll easily take a set of f/2.8 zooms over fast primes any day of the week, but as been pointed out, some venues just don't allow flash photography, which is where the primes come in. Unfortunately, high ISO isn't always the answer. Yes, it's getting better, but it's still not as good as shooting at 800 or less. One thing to remember about weddings is that there simply aren't any re-takes. It's a now or never situation to get the job done right. I'll put my trust in fast primes at lower ISO lightyears before I'll trust even f/2.8 zooms at higher ISO. Of course this is only for those places where it's needed. Honestly, 90% of the time, it's smart to have 2 zooms (a 24-70 and 70-200 f/2.8), a 24mm f/1.4, a 50mm f/1.2 or 1.4, and an 85mm 1.4. Sometimes, a 14-24 is invaluable for really wide group shots, or even switching it out for a 14mm f/2.8 prime if desired.
At the end of the night, it boils down to this. When it comes to wedding photography, it's the photographer's livelihood and reputation on the line. The better your reputation, the more income you'll generate. One simply can't afford to botch a wedding by always trusting a zoom. Yes, I love my zooms, and yes, as long as flash is permitted, you can be sure I'll be using them. But when you can't, a good, old fashioned prime lens will put you where you need to be.
One more thing to add. It's ALWAYS a good idea to go to the venue BEFORE the date of the wedding and talk with whoever is in charge. Ask questions about where you can and can not be, if you can use flash, and any other questions you may have. The rehearsal is a good time for that, if you can make it. It'll also give you a sense of the venue and how it'll be lit