I would like to know this as well. If one excahnge changes their price, wouldnt all others? Otherwise it would obviously look fake.
Here is what I see going on with coinbase:
![](https://ip.bitcointalk.org/?u=http%3A%2F%2Fpuu.sh%2F5GD6J.png&t=663&c=Gw5Wv0Xv43f-EA)
There is a $20 difference.
Exchanges don't set prices. The buyers and sellers set the prices.
The difference of $20 at Coinbase seems about right. Aren't you aware that Coinbase charges a 1% fee?