I don't even know that conspicuous consumption has all that much to do with it, for a lot of people. I am not conspicuously consuming for my wedding (and have, in fact, tried to cut a lot of corners). There are some things I've spent money on that I maybe didn't have to, but the vast majority of those things has been with the idea of providing better hospitality for my guests.
The reason why my wedding is costing several thousand dollars is simply because that's just what it costs. It's in a large city, in one of the most urban parts of that city, and things are just expensive there. Half the budget, easily, is food. Actually, at this point (because it's looking like it may cost less than we thought), it may be more like 2/3 catering expenses.
Even my rehearsal dinner (which includes almost as many people as the wedding) is going to cost somewhere in the neighborhood of $1000. And that's as bare bones as it can possibly get -- food from inexpensive restaurants in metal pans, plastic table clothes, paper plates, and an iPod for music.