Each exchange is a marketplace, and has its own price discovery process. There are specialists who arbtrage all the time not just in the cryptocurrency exchange markets, but all kinds of other financial instruments, and even physical goods, and services that can be delivered electronically. In fact, the reason why I live in eastern europe, aside from that I like it here, is the arbitrage of many prices for necessities, which has a price differential due mainly to taxation. I earn the money in markets where my labors are worth more, and then I can spend them here, where the prices are lower.