為甚麼有些currency特別高息?

Interest rates offered to currencies depositors depended on the official interest rates given by the respective central banks in those countries. For example, the AUSTRALIA PRIME RATE offered by Reserves Bank of Australia is 6.5% while NEW ZEALAND PRIME RATE is 8.25% by Reserves Bank of New Zealand.
The banks just offer the interest rates those are given by the respective currencies' central banks, they will not decide the interest rates.

紐元(NZD)、泰國銖(THB)、南非蘭特(ZAR)、英磅(GBP)等;不同銀行亦有高低的分別。

http://www.whbhk.com/whb/action/rate/whbRate.do?id=fc_deposit_rate&lang=zh-hk
http://www.hangseng.com/c_rate/interest_rates/zar.asp
http://www.ccbhk.com/chinese/rate_inter_frame_a.htm