the idea as well that you should try to work out what others can afford and only base round that is also flawed because it assumes you can second guess what other people can afford.
Before having DCs, I was earning £35k ish a year, after tax/deductions that left me with about £2,200 a month, my share of bills came to £1k a month, rail card was under £200 and so I had £1k of money just for myself each month (ah, the days of drinking in Belgravia and ordering ludicously expensive G&Ts without thinking about it). I could easily afforded a posh holiday like that, I would also expect other friends living in similar sized properties doing similar jobs to equally be able to afford a holiday that's round £1k. (whether they'd want to go, or could get the time off, would be a different issue). We did do group holidays (although not hen ones) that where in the £2k each mark and thought nothing of it.
But if you have a family to keep from double that wage, you could be left with only a few hundred pounds a month left over for both adults to have as their personal spending money, and holiday leave is precious family time.
I hadn't thought about just how expensive childcare and family costs were until I had DCs, and I hadn't thought how cheaply some people who bought their houses 10 years before we did could live. It's not enough to try to guess what people can afford based purely off their job. BIL is on around £100k a year, however they've just bought a house that's about the same size as ours but cost them £200k more because they bought later than us, SIL is a SAHM, they moved in from a furnished flat and so had to buy all their furniture recently (and are paying that back) and SIL has family who have been in financial trouble that I know they are helping out. On the face of it, BIL and SIL should be far richer than we are, but I think they actually are going to be struggling for the next few years.
On the other hand, DH and BIL's cousin is earning just over NMW but she has no DCs and lives at home with her parents who take no money off her for rent or food, so she actually has more spending money and regular holidays than her "rich" cousins. (I was most jealous of her 4 weeks on a Greek island in the summer) I can quite easily see if she got married she'd arrange a big hen do and be surprised that others couldn't afford it. She dosn't get how much life costs.