There are American traditions and family values, but they are more subtle than what you'd see in other cultures, and you wouldn't necessarily see them unless you were the person getting married or were intimately involved with the wedding (like a maid of honor or sibling of the bride or groom). There's no one way to do things here, largely because everyone has different ethnic backgrounds and people value other people's individuality. Some weddings are formal, some are casual. Some are tiny, some are huge. Some are religious, some are officiated by Elvis impersonators. We did things at my wedding, because I'm of Slavic decent, that you wouldn't see at a wedding of someone with Italian decent. There's also regional differences--like, here in Western PA, it's normal to have a cookie table, whereas in other parts of the country this isn't done. That said, there are common "rules" for all weddings, and there are PLENTY of etiquette and taboos (just read more in the weddings section of Yahoo Answers). Just because you haven't picked up on them doesn't mean they're not there.
In other countries, people have more time off to spend 3-5 days partying, and preparing for the party (been there, done that, was very fun). In the U.S., most people don't have that luxury. They run from work to the rehearsal on Friday night, spend all day Saturday at the wedding, and sometimes have a brunch on Sunday, and then run to work on Monday. Most of us get 2 weeks off a year, and are very selective about how we use that time.
Not to mention, throwing a days long celebration for 300 people costs tons of money. They average 1 day long U.S. wedding costs $30,000--about what an average person makes in an entire year.