You cannot eat wealth. A good part of wealth is tied up in tangible things like buildings, infrastructure, etc. A lot of Japan's businesses cannot operate to produce what they need right now. One of their largest companies, Toyota, may have to stop building cars in the US and other countries, because Toyota cannot supply some of the components that are made in Japan. They DO have a fiancial crisis, and more importantly, a humanity crisis.
We do not really know the true extent of the disaster yet. The disaster is larger than the ability of the people (government) to handle. It is mind boggling. There are thousands of people without food, safe water, shelter, adequate health care, etc. Japan needs help and many Americans (and other countries too) want to provide help. Also, many Americans (and other countries) work with or for Japanese companies.
During Katrina many Americans donated. Much more than any other natural disaster than I can remember.