This wasn't a calculation thing nor weighing of profits. It's absolutely tradition and part of many cultures that gifts at the wedding are monetary. Certainly this is a HUGE asian thing so much so that they even have special envelopes for it. I don't know anyone who has planned a wedding looking forward to profits. Profits happen and sometimes they don't. The bride and groom will probably want to open everything to know who to send thank you notes to and what to write in them (if making them personal). So these are observations related to me from others.
I'm going to Portugal to get married and I don't care/expect anyone traveling to bring or give a gift at all.
This post also wasn't about judging close friends. Every wedding has a lot more people involved that can hardly be considered close friends. Case in point this wedding I'm talking about. I believe a couple of the guests that brought nothing were co-workers in senior positions at the bride's company. I'm sure they weren't invited as any type of cash-grab. I don't know them and I don't know why they were invited.
As I mentioned, I live in a very multi-cultural area so I've seen it all. Many Italian weddings hire off-duty police on site to protect the cash as well as act as general security. A few years ago there were a string of wedding robberies because on a Saturday night hitting 2 or 3 weddings they could pull away with anywhere from $50 to $150k.
These friends didn't expect to make money, even though many weddings here are huge cash cows. But it was pretty insulting that some people didn't bring anything at all. The per-head cost was about $150. That's not renting some space at a community center and serving sandwiches. Open bar all night - something I know a few of these people took advantage of to the extreme.
Anyway, I would just never (not ever) go to anyone's wedding without at least covering the cost of my plate. I consider this to just be practical etiquette.
If I went to someone's wedding at their house I'd still likely bring cash unless they asked specifically for something else. Probably at least $100 per person attending ($200 for myself and a guest for instance). If they were close friends I'd give more. I've done gifts in lieu of cash at the weddings of two friends. In both cases it was 4 of us getting together to buy a TV that cost about $2000 - that was in the early 90's.
When I go to someone's house for a general party I always bring something, not cash of course. Generally always a bottle or two of wine at least. If it's someone's birthday I wouldn't show up without a gift. A wedding is not simply a get-together or a simple party. At least not the formal weddings I'm talking about. An "average" attendance is about 130 to 150 people and a sizable one is over 300. Anything under 120 I'd consider a small wedding.
I suppose there's always going to be issues when mixing cultures that don't share at least some common customs. But for me, weddings are about the bride and groom, so personally, I'll conduct myself according to their customs rather than my own if that's appropriate. That includes dress or any ceremonial functions of course. If it's my own custom to wear a T-Shirt and sweat pants, I'm not going to show up to someone's wedding in that get-up. Likewise, what kind of a tool shows up to someone's wedding wearing a white dress? That's also extremely rude (someone did this last weekend as well).
Anyway, this wasn't my wedding but I was just shocked that someone would think it's ok not to bring a gift of any kind. And also thought it was unbelievable that someone would complain about the customs/traditions of the bride and groom's culture when they were being invited. My suggestion to them would be to simply decline the invitation if they felt so strongly about it. Don't show up with a humidifier because your husband sells them in his day job and it's the gift you give to everyone. Ugh.