经济实力好

USD是世界通用货币.JPY是公认的小美元,它跟着美国爸爸混.

在经济体系不好的情况下,JPY一直很妖孽的在升值.

Two factors:

1) Compared with other ecomonic body, US and JPY have highest credit ( no default history on their Gov. bonds) and are top 2 largest developed.

2) The majority of international "hot" money are US and JPY private investors. Whenever they think the risk is escalating, they will dump foreign assets, send money back home. As you know, its natural that people feel safe when they at home! (Of course, its another story if you have a sassy wife/girlfriend at home -:)  Just kidding! No offense to girls!

BTW, if RMB is freely float, RMB will have same status as USD and Yen! (That's what I believe)

避险的说法值得怀疑，日本现在经济这么差(http://www.moneyweek.com/investments/yen-shrugs-off-grim-economic-data-42305.aspx)，一个避险解释不清。