Not much need to make internal transfers - London and Hong Kong are two of world's largest financial centres so there's plently of local work to do and it's not exactly hard to collaborate with colleages in NYC from London when there's a good 4/5 hours a day of overlap when both offices are active.
Looking at salaries is misleading anyway - companies like Jane Street do most of their compensation as bonuses rather than salaries. Having worked in the proprietry trading world, salaries are generally on the low side, but your bonus can be anything from 50%-100% of your salary upwards. It differs a fair bit depending on what you do - a traders' bonus will be more volatile and pegged to their performance that year, a back office dev will propably have a more stable bonus year to year, but not as large.