Why the large oil price differences?

I previously misunderstood the cause of the spread between West Texas Light Sweet price of oil and the Brent price, which has been over $10.  I was under the impression that there was a potential corner in the Brent market. Finally I heard this piece on the radio, and actually uderstood what they were talking about.  Here's another article on the situation at OilSlick.com.  From the story:

With a working capacity at 40 million and current inventories at 38.3 million that does not leave much for speculators to work with. If there was an accident downstream from Cushing and they had to halt deliveries out of the Cushing inventory they need some surplus capacity for that kind of emergency.
Compounding this problem is the rising flows coming from Canada and the oil from the Bakken taking up refinery capacity and leaving more oil at Cushing. Transcanada Corp just completed a new arm of its Keystone pipeline to connect Cushing to the flow of crude from Alberta. That is going to be 150,000 bpd of new supply headed for Cushing.
This is going to increase the pressure on WTI as Cushing storage fills up and leave traders nowhere to turn. The problem will eventually be solved when Transcanada completes another pipeline to the Gulf of Mexico in 2013. This will relieve some of the inventory pressures at Cushing but that is two years away. That is a lifetime in the futures market.
With the Bakken ramping up from 350,000 bpd to 500,000 bpd over the next two years and Canadian oil sands production increasing the pressure on the WTI price is going to be immense. Odds are very good the spread between the Brent and WTI contracts will become even wider.
The Brent contract is primarily North Sea oil and unlike WTI it can be delivered anywhere in Europe.