What you're doing is arbitrage, and it isn't anything new or special. In order for it to work though, you need to be able to move assets quickly and you will need to be able to buy and sell assets quickly.

For arbitraging coins:

1. You need coins that actually have volume. Sure, the price on one exchange may be higher than another but that doesn't do you much good if no one is actually selling or buying the coins. There are plenty of low value coins that have significant exchange price deviations but their volumes are so low you can't actually arbitrage them.

2. You need to be able to move coins quickly between exchanges. If you have to wait 30 minutes for your deposits to clear then there's more than a good chance the arbitrage opportunity will vanish (especially with heavier traded coins).