There are tea ceremonies, and there are ceremonies involving tea. A Chinese wedding is one of them, at least as practiced in Guangdong (I’m not sure about other areas)
What happens in a traditional wedding ceremony goes something like this — the couple walk into the main all where everybody is already there. The parents of the groom are present in the house, sitting facing out. The couple walk up to them, and then they bow three times. Once to the heaven, once to the parents, and then the third to each other. Then they serve a cup of tea to the parents (kneeling, of course), and in return they get some good luck money in a red bag and some sagely advice, and this is basically what it takes to get a bride to be accepted into the family. I heard in Korea it’s not tea, but wine, that is served, but the idea is pretty much the same.
I don’t know if there’s a rationale behind the choice of tea other than the fact that it’s the most common drink and that many Chinese just can’t handle wine. But perhaps there’s a sense of domesticity in drinking tea that wine doesn’t do — you drink wine to celebrate or some such. Tea, however, is something you drink all the time. Marrying into a family is going to be a full time affair — you become part of family, and so perhaps in this sense, tea is very appropriate.
These days (such as the wedding I went to today) the bowing no longer takes place, but at least in HK the tea serving gesture is still generally done, however haphazardly. Except that nowadays, they are often wearing a tux and a qipao, usually (kneeling in a wedding dress can be a difficult move, methinks). The parent of the bride also get served these days. Even though circumstances changed though, there’s still some sort of symbolic power that this ceremony holds, so that even this thoroughly westernized society in Hong Kong still performs this. It’s this kind of thing that makes Hong Kong quite unique — this is probably the only place on Earth where both Christmas and the Buddha’s birthday are both public holidays. East meets West at its finest.