Most of the discussion on that Reddit thread is uninformed crap.  For a variety of reasons, it is completely reasonable to expect there to be different supply / demand equilibrium in different global markets.  Arbitrage should equalize the global differences, but sometimes there is not enough capacity in the arbitrage channels to equalize big differences.  By that I mean the FIAT cannot move fast enough around the world.  In an attempt to not run out of coins for sale, Coinbase had to raise their buy and sell prices.  I had a pile of cash on Bitstamp that had been sitting there for quite some time.  When I saw the favorable spread, I quickly bought coins on Bitstamp and sent them over to Coinbase to sell them for a higher price, thereby 'delivering' coins to Coinbase, who in turn could 'deliver' them to its customers.  Coinbase makes their 1% as always, their customers enjoy the convenience  and safety of a U.S. based, ACH-bank linked broker, and arbitrageurs like myself enjoy a little payday for the risk and hassle we incur by setting up accounts with foreign excahnges AND by leaving money sitting there for a long time.  For example, the money I had on Gox is not doing so well these days.

But, someone has to take the risk of leaving money or coins on exchanges.  If the was no buffer, we would see some really crazy volatility.