DaraMahini, I doubt that anyone is going to buy the line that your meaning in the OP has been misunderstood due to English not being your first language. As TheButterflyEffect has noted, your tone is pretty consistent throughout the thread title and OP: "just tacky", "quite rude", "forking out". If you have an opinion that is offensive to another culture, and you decide to post that opinion anyway, please have the decency to either stand by it or apologize for its offensiveness. Claiming you were misunderstood when you so clearly were not is just cowardly.
tadjohndoryp in my experience wedding guests don't tend to bring gifts to the wedding itself. Generally there is a bridal shower, in which case yes, gifts are opened and people are thanked in person just like at a baby shower. Alternatively, people may drop off gifts, give them through a family member (like the bride's mother), or post them to the newlyweds up to a year or so after the wedding has taken place. If a gift is given in person, then yes, it is generally opened in person so that the giver can be thanked. In all of the above cases, a written "thank you" is also sent to the giver.
The wedding rehearsal is a dry-run of the wedding itself, yes. For church weddings, the people attending the rehearsal would be the bridal party, people with a role in the service (readers, eucharistic ministers, etc.), and the immediate family of the bride and groom. After the rehearsal, where people make sure they know their role and ask any questions of the officiant, everyone goes to dinner together, often paid for by the couple or the family, as a way to thank the wedding party. The couple may give token gifts to their bridesmaids/groomsmen etc. or to one another, but gifts for the bride and groom are not given by guests at the rehearsal dinner.
On the subject of weddings, I'm so glad that Bue made the point about "evening only" invitations in Britain and Ireland. I live in Ireland now, and I was very taken aback the first time I was invited to only the afters of a wedding. It did feel like I was on the B-list, and as it was a church wedding I thought it was even more bizarre that I wasn't being asked to share in the celebration of the sacrament, but was welcome to join in the drinks after and, presumably, to bring a gift for the couple.
It was out of step with my own (American) understanding of politeness and normality, so I can understand that people outside of American culture might feel the very same way about baby showers, or wedding showers or trick-or-treat for that matter. But as I became more familiar with the way things are done in Ireland, I grew to understand that it is not insulting or gift-grubbing for people to invite some wedding guests to the afters only. It is simply the way things are done here, so people who are used to it don't look for rudeness and tackiness where none is intended.
Some people think that watching "Friends" and "Sex and the City" makes them sufficiently knowledgable on American culture and traditions to make declarative judgements about them. I think that's why American traditions are considered fair game for culture-bashing in a way that other countries' traditions are not.