Quite right, @eddieb 
To address another point of confusion, the data you found were from the Bank for International Settlements (BIS). They publish a survey of the forex industry every three years, so the next one will come out in 2019. Here is the complete report from 2016: Triennial Central Bank Survey of foreign exchange and OTC derivatives markets in 2016
The five places you mentioned (the UK, the US, Singapore, Hong Kong and Japan) are global currency hubs. Below is a useful chart from The Telegraph.
That means forex market participants around the world ultimately have the bulk of their liquidity provided by banks in these major financial centers either directly as is the case with larger forex brokers like us or indirectly as is the case with the smaller forex brokers, individual retail traders and institutional traders who are clients of FOREX.com and our parent company GAIN Capital through its GTX division.
We discuss this flow of liquidity from the interbank market makers* to large forex brokers (market makers like FOREX.com) to smaller forex brokers and retail traders in this post: Who is the counterparty in an exchange?
*“In order to be considered an interbank market maker, a bank must be willing to make prices to other participants as well as asking for prices. The minimum size for an interbank deal is $5 million, but most transactions are much larger, and can top $1 billion in a single deal. Among the largest players are Citicorp and JP Morgan Chase in the United States; Deutsche Bank in Germany; and HSBC in Asia.” - Interbank Market Definition