> I don't know if I believe the price goes up that much because of the fear of [an overly zealous wedding party member]
> But for a wedding cake, people want 5 9's. They want enterprise Cake, that's always available and exactly as they expected.
I see those two things as related, I guess. Nobody knows the difference between 2 9's and 5 9's until the service goes down or something goes unexpectedly.
> If I was working with a vendor, a plain-old regular cake with 2 9's availability would be fine for me.
Unfortunately for the vendor, since you're not ever going to be a repeat customer they have no idea which type of customer you are and have to assume you want 5 9's even if you're saying otherwise - or that you want 5 9's for the 2 9's price. The opposite of a lemon market, I suppose (a peach market?).
Look at it from their perspective: The worst case scenario is they give you the 2 9's price but you expect the 5 9's and complain loudly when you don't get that.