The other strange one is SGD vs AUD. How would the Singapore economy be stronger?
Apples and oranges. It's economy is not at all dependent on commodities so in many ways is very different to the Australian economy. Besides that, the SGD is neither fixed nor freely floated (like the AUD). It's value is managed by the SG government, as much as it can. SGD has devalued against USD (by about 15%), but nowhere near as much as AUD.