Oh come on, that's obviously false. The same wikipedia line says that "70–85% of Japanese profess no religious membership or personal religion."
Didn't say it was the truth, just that Buddhism is still big in Japan. The Japanese relationship to religion is complex and not something you can easily measure. Membership is not a possibility in this context.
Still, Buddhism is the majority religion in three 50 mio.+ countries: Vietnam, Thailand and Burma and it is a cultural factor in countries as important as Japan and China.
Regarding Wiki: Its says surveys show that 18-20% of the Chinese population are Buddhists, that looks legit. Regarding Taiwan it says 90% are Buddhists, so that would add Taiwan to the list, but maybe that's an exaggeration?
Tibet is still majority Tibetan (barely) AFAIK, and it is a country, despite not being an independent one.