They made a promise to deliver bitcoins at a certain price and on a certain date. The original poster's issue is equivalent to Amazon promising 2 day shipping but the book came a few days late.
Unfortunately, for the amounts involved its borderline not worth pursuing. It's too large an amount for most small claims courts, and too small an amount to justify the time and cost of civil litigation (unless it settles at the very early stages). Indeed, based on Coinbase's record (refunding purchases if BC prices increase rather than executing the transaction), it's very likely that they are factoring this arbitrage into their business model.
The value of BTC lies predominantly in the market value.
So the book analogy is ridiculous and patronizing.
As I mentioned in a few other comments, just seems to me that frustration over the Coinbase's error and frustration over the price swing are both being heaped only on Coinbase.
I've had great experiences with the product and company, I would hate for this particular screw-up to be seen as representative of their overall service.
You don't need to be called an exchange or sell currencies in order to be financially liable for delays; and the more perishable/volatile the product is, the larger the possible liabilities.