It looks like SPDR GLD (a gold-backed ETF) can be purchased on 5 different exchanges: US, Mexico, Singapore, Japan, Hong Kong. What is the difference between these? Are they just 5 different ETFs that all track gold, or are they related in some way? Why is there a need for more than one, when many (most?) investing platforms these days allow investors access to multiple markets?
None. Shares can be traded on multiple exchanges in multiple countries. There is need for more than one - heck, why are there multiple supermarkets in one city? Or even in different cities. Not every broker works in every country, exchanges are in constant competition. There is no NEED for having more than one exchange on the whole planet to start with - if you look at the definition of need. They still are there.