I always used to judge people who spent extortionate amounts on their wedding but once you try to get married on a reasonable budget yourself, you realise all the little costs add up. Unless you're willing to give up a lot of the usual traditions it is not easy to do it on a budget.
A fairly modest barn venue in my area quoted us £6k for the reception and food just for 50 guests - not even a massive wedding! We found somewhere more affordable in the end.
The problem with this question is that people will include different things in their amount. I'm not sure if everyone is including the cost of wedding rings count as part of the wedding cost, and what about engagement rings? Did your wedding party pay for their own dresses and suit hire and is this included in the amounts people are giving? All this stuff adds up and makes a it difference so someone's £3k wedding might have cost double that amount if they forgo to include all these other costs.
Church wedding itself: about £250
Reception venue and food for 50 people: about £3k
Dress, suits etc for bride, groom, bridesmaids etc: over £2k total
Flowers: £100
Photographer £300
Cake: £50
Jazz band: £1k
Wedding rings: £1200
I can't remember all the other details but I'm sure if you added it all up it would come to at least £10k. As you can see we splurged on some things (dress, jazz band, rings) and went cheap on others (photographer, cake, flowers). If we hadn't got friends to do the cake and photography, and if we'd spent more decorating the venue, that's already another £2k or so added to the cost! To be honest I can easily see how it ends up adding up to £20k or more for some people.
I find some people really naive about costs though - I've got friends who claim they'll have a cheap simple wedding with a marquee in a field or back garden and a BBQ or hog roast. They don't realise that approach can easily end up costing thousands and you have to hire bloody everything from the marquee to the cutlery to the chairs and god knows what else!