There seems to be lots of confusion on this point. Part of it is the social meaning of religion, maybe a slightly different definition. Or, say, exclusivity. It is true that the Japanese will most often turn to a Buddhist temple for funerary needs. For weddings they might go to a Christian (or faux Christian) church or a 'shinto' shrine of native gods. So maybe it is fair to say most Japanese are not *exclusively* Buddhist, but even many Buddhist clergy accept this and do not find it strange. It is also fair to say that not many Japanese Buddhists go to the temple once a week, sing hymns, make a monetary offering, listen to a sermon and then come back for the same thing the next week. For one thing, Buddhist temples were around before the seven-day week in Japan! The Japanese sense of order requires a decimal system wherever possible, so a 30-day month was conveniently divided into three ten-day periods. It is still common for temples to have regular services at ten-day intervals, for example on the eighth, the eighteenth and the 28th. But even weekly or monthly temple attendance is probably low on the list of priorities for most lay Buddhists. The services might feature sutra recitations and a sermon (法話 'houwa' in Japanese, corresponds to 'Dharma talk'). There are some temples that actually have congregational hymn singing, but most of them don't, I think. Even more than attending services, for most people the most important thing is to drop a coin in the box even if you are just passing through the neighborhood temple grounds on your way somewhere else. The polite thing to do is pause in front of a temple or statue, put your hands together (合掌 'gasshou') with a bit of a bow, and drop a coin in the box, which is placed out in front for your convenience. The value of the coin seems to be completely irrelevant. Maybe lots of people are cheap like me, putting in the smallest coins except on special occasions--something people never talk about! LOL I have never heard of anyone stealing from these offering boxes--some security efforts are made, but they are minimal. Either thieves don't want to mess with small denominations of coins, or maybe they are Buddhist in the sense of knowing it is extra wrong to steal from a temple.
That being said, if you keep your eyes open, you can see signs of Buddhism everywhere. Major roads in Tokyo that have been highways since the old days still have many old statues of Jizo, the protector of travelers, still lovingly tended with fresh flowers, offerings of water or sake, and red caps and bibs. Even the business areas filled with office buildings have small temples tucked away here and there. Once you are aware of such things, you can feel a fairly steady Buddhistic 'hum' as you travel around the country.