I know I am late to this thread but one thing that sticks out to me is the number of people saying 'Just go get something if you're hungry, what's the problem?!'
1)Not all weddings are held in places that sell food. Some bars don't even sell snacks/crisps, especially smaller ones or ones set up/designated for booze only for parties. I think It's rather ignorant to say 'nip back to your hotel room and have a sandwich!' You might be in a stately home, someone's back garden, a barn or a venue used solely for weddings. You might have been there a day or so already-where are you going to whip up a sandwich from? The hotel may not be serving food at that time and you'd look a bit odd ordering food when the B&G had put some on anyway and eating it sitting at a table in the middle of people mingling. Also, I've only ever been to ONE wedding that was held in a hotel, and I've been to dozens of them.
2)Not all weddings are held near towns. Some are in the back of beyond and driving off to pick up a sandwich would be an hour long trip (or more)-If you don't know the schedule/timings you could miss something important, perhaps even the food.
3)Not everyone drives.
4)If you're 2 glasses of wine in and feeling peckish, you can't drive anyway. Plus IME a lot of people don't drive to weddings, they may have got a lift or a bus so they can consume alcohol, It's a party, It's what (a lot of) people do.
Carrying snacks is the best idea IMO/E but, It's not always really practical. Especially in a fancy frock with your little clutch bag. If you have children with you, that's different and much easier as you'll (usually) have a larger bag with you. I do agree that if you're going on a long day out (anywhere) and aren't sure where to get food from, It's never a bad idea to prepare for that.
I can't remember how many have done it, but I do remember the last two
I went to and they both had a 'schedule' sent, it was on the backs of the invitations. It really helped me prepare for when to eat, how much alcohol to drink/not drink etc, nothing worse than that sick feeling. I know some posters have said they'd find it 'uncouth' or such to do that but I definitely prefer to know what's happening, before I go anywhere, wedding or not.
I am not particularly 'posh' and have always called it a wedding breakfast and so did the last two weddings I went to. I can't remember about others but It's a tradition referring to religious weddings where the couple would fast but aside from that, breakfast literally means 'breaking a fast' break-fast. If you worked late and don't eat anything the next day until 1pm, you're still breaking the fast from when you last ate/slept. It has never meant 'meal eaten of a morning'.
I don't think I am greedy and I am not overweight but going from morning until 2100 (as a poster said upthread) without food, I would be feeling lethargic and ill and probably not much like partying. Wedding guests are just that, GUESTS. Look after them!
The two best weddings I have been to did provide a schedule so people knew where they were at. They were also vastly apart in terms of expense and venue.
Both my old university friends but one is a homely/hippie type and one is very corporate in her lifestyle so they were extremely different.
The former had a traditional pagan wedding in the early afternoon. We could walk from our hotel to the venue which was in the town, and everyone stayed at the same place if they didn't live close by. Reasonably priced. Ceremony, then straight to a large barn-type venue with a bar. Copious champagne on the tables, and I was VERY lucky to be the only one on the table that liked it (hic) then a simple buffet came out into a central table. Plenty of choice and plenty of food for everyone. Multiple pasta salads, curries different types of bread, meat and cheese, lots more, I forget. It was restocked throughout the day/night until everyone had had enough (and they checked)!
Short but lovely speeches, cake then organised/free dancing that went on until 11ish. Perfect. They'd put taxis on to get people back to the hotel. She told me how much it cost, about the same price as a breast enlargement (I am sorry, I cannot think of anything else that is about that price)! 
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Latter. Very 'naice' venue in the middle of nowhere. Must have cost an absolute fortune. Everyone in themed period costume. Wedding at 1pm. Mingling while photos were done for about 90 mins, canapes and plenty of them. Speeches (again not too long) and breakfast at around 4pm, more than enough food, 4 courses, traditional english food, with a vegetarian option. Wine on the tables and more than enough of it. Everything there over by 630 ish.
First dance and then dancing again until the last person left. Pizzas and other options put on around 2130.
I wasn't cold, hungry or bored at either of them and they're my favourite ones out of every wedding ever because of that. I cannot say the same for the rest of them, and it was nothing to do with expense or lifestyle of the couple.
Having said that, I think the PP who pointed out that people who don't tend to host/attend many events may not be the best at organising them. They're essentially in charge of something they've not really experienced before.