Bitcoin Bid/Ask and Arbitrage

In my previous post, The Bitcoin Price, I bought a small quantity of bitcoin on Coinbase and then wondered, 'How was that price determined?' I started searching for bitcoin bid/ask quotes and found dozens of them on Bitcoin Markets [bitcoincharts.com], sorted in descending order by 'Volume'. Since Coinbase wasn't shown, I checked that site (I could have done that first) and found the question, Why is the price on Coinbase different from other websites?

The price of bitcoin on Coinbase is based on the average of a variety of exchanges, so sometimes our price differs from any one particular exchange. As the price between different exchanges stabilizes, our price will be naturally self-correcting.

That answer implies that some sort of arbitrage is active. I started searching for that and found Bitcoin Price Arbitrage Explored [cryptocoinsnews.com; dated '04/11/2014' (11 April or 4 November? I really dislike dates written like that)]. The essence of the article is simple.

Pure arbitrage in the Bitcoin exchange market is not viable because of the slow transaction mechanism imposed by the blockchain.

I found similar conclusions on other pages. Putting it all together, the price on Coinbase is whatever they say it is.