Why would the caterer do this?

Can anyone explain to me why the guests at a wedding would be asked to wait for the bride and groom to finish all their pictures, freshen up and appear at the reception before being served ANYTHING to eat or drink or even allowed to serve themselves from the buffet or bar? I have always thought that people who are invited to a wedding were the GUESTS and that a reception was mainly for their refreshment and continued celebration with the happy couple. Now it seems that people are invited only to be the audience to the MR & MRS SMITH SHOW with little or no consideration shown to those who attend. I was recently chastized by a caterer for trying to get a bottle of water off the buffet table for the groom's 74 yr old grandmother after she had trekked down two flights of stairs and across a wide expanse of sand to sit through a 45 minute ceremony in the wind and salt spray only to make the return trek, alone as everyone else was having their picture made, because she needed a drink of water. The table attendant just pointed to a sign (yes, a little plastic sign on the table) that said 'Please wait for the bride and groom' and shooed her away like a child when she tried herself. Being made of sterner stuff, I went back over and got one for her only to have the head food slinger come out from behind the table and actually try to grab it OUT OF MY HAND all the while whining 'didn't you see the sign?' Why would ANYONE want their GUESTS to be treated in this manner? When I spoke to the bride's mother she just said, 'that's the way they did it at my other daughter's wedding last year. I thought it was a new custom.' Well, is it?