Mind you, the fare that is shown on the website is the blended average fare for 2 people, it's not like the first person is the price on the website and the second person is 75% off of that.
So for example on a random cruise I pulled up, the Celebrity website shows $1,079 per person. In reality, when you go to book you see:
Guest 1: $1,786
Guest 2: $371
So the total is $2,157 or an average of $1,079 per person.