Erkki, thanks! When I puchased this optical gem, I wasn't sure how long I would keep it. But I was pretty much hooked with the lens and have been enjoying way more than I had expected.

Frank, that is a BIG question! Indeed the original purpose of the New Year's vist to the shrines is to offer prayers to our ancestors. But we don't only visit Shinto shrines but also Buddhist ones. Honmon-ji shrine is the largest Boddhist one in Tokyo.
There have been several regimes and governments that politically tried to merge Buddhisms into Shintoism. People, on the other hand, don't necessarily consider these two as separated religion. Shintoism is more like Shamanism. (I found the concept of Shamanism is very common throughout the world, by the way.) And the influence of Shintoism have sneaked into the concept of the Buddhism throughout the history of Japan. As a result, "our" Buddhism is quite unique and different from, say, the Tibetan Buddhism which is much more closer to the original Buddhism. Actually the ancestor worship is an idea of Shintoism, not Buddhism. Originally Buddhism has nothing to do with the ancestor worship. The essential concept of Buddhism is "samsara" (a never-ending cycle of life and death). People die and reborn, which is repeated until they (we) reach the state of nirvana. So, the ancestor worship makes no sense: the ancestors are also in the never-ending cycle!