Successful and consistent arbitrage is a catch 22. If there was an easy way to do it, everyone would do it. It would be conventional practice. However, supply and demand is an economical law, and its forces in this case are no exception. If there's a flood to buy on one exchange and sell on another, it would quickly balance out. Prices would equalize among exchanges long before most sellers could profit on the spread.
However, exchanges and users should still hope for arbitrage to be easier. First, it would add stability to BTC price overall, not just for individual exchanges. Second, it would open competition for exchanges to offer better features, such as advanced order types and obscure altcoins.
One such exchange has developed a method to make arbitrage easier. It's called Tether, a centrally controlled cryptocurrency with a fixed value on par with the USD. I personally think it's a great and fascinating idea, but I have far too little trust in the company controlling it. Frankly, I wouldn't trust it unless it was run by a US or European bank.
All this is to say that if you do it successfully, you probably got lucky.