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It depends, and I think the line should be drawn on the basis of how food issues break down. There are times when it is OK to impose food restrictions and then other times when it's just plain rude to impose food restrictions.

When it's OK / understandable to impose food restrictions:
1) Budget. you just can't pay for it. If all you can afford are carrots and celery sticks, then for the love of God, keep the proceedings SHORT. Similarly, if you can't pay for beef, but can afford to offer chicken, then no guests should have a gripe about there being beef in stead of chicken.
2) Food allergies / intolerances. If the bride and groom can't eat it, then guests should be understanding of the bride and groom not serving food that they can't eat. Of course, there is kind of a difference between say, a nut-free wedding reception vs. no ice cream sundaes because the happy couple are lactose intolerant.
3) Religious / moral / ethical reasons. If the bride or groom do not eat certain foods due to religious / moral or ethical reasons, then I don't think guests (close friends and families) should expect the couple to compromise their beliefs.

When it's NOT COOL to impose dietary restrictions on guests.
1) Food preferences - If the couple happen to be very adventurous eaters, the money is just going to go to waste and it's rude to guests who won't eat it. Similarly, along the same vein, I think if a vegetarian is a vegetarian for personal health reasons, I'd probably be annoyed as a guest if all of the food was vegetarian. It's fine if you want to adhere to some health standard, but don't impose one's issues onto others. In this case, you still want guests to have a good time, no? I also think most vegetarians do have friends and family who happen to enjoy meat, so I imagine a good number of vegetarians are pretty flexible in this regard.
2) Being cheapskates. I wouldn't say that they have to go overboard in offering a buffet of culinary delights, but at least feed guests something that the couple would be happy to eat. Also, I think if you can afford it, offer an open bar for at least an hour. Some guests will spent considerable time, effort and money to attend the wedding (one in which they may not know too many of the guests). Don't cheap out on the alcohol.

FWIW, I'm an omnivore, but 6 out of the 9 offerings at our wedding were vegetarian. 4 of the 6 hors d'oeuvres were vegetarian (hey, one was mac and cheese) and they were all tasty, and the salad and dessert was also vegetarian friendly. For the main course, folks had the choice of salmon or beef. (I chose the beef, as I only eat salmon raw, rare or smoked...) And of course we had an open bar. I did insist on Brooklyn Brewery beers, but that really wasn't too much to impose on my guests, I don't think.

uh... how was the actual Clover brewed coffee?

I won't ever order filet mignon. Rib eye, porterhouse or strip steak, and of course, no more than medium rare. I would never serve or cook any steak that was cooked beyond medium rare!

Tuna - seared. I was with someone at a steakhouse who ordered a blue fin tuna steak and he ordered it cooked medium. I couldn't help myself and leaned over told him in no uncertain terms that a tuna steak cooked "medium" would be overdone. I still shudder over the memory of medium cooked tuna.

Salad dressing -yup, homemade. Preservatives, sugar and emulsifiers in the storebought kind - gross, no thanks.

Finally, not exactly a food prejudice, but unless it's a restaurant that is known for one awesome dish, it drives me nuts when people in a small party order two of the same dish. The worst is when it's on a date! What? you can't share? Try a different entree or appetizer, go ahead! Explore the menu!