I think whether or not this is wrong depends entirely on whether or not money as changed hands at the time the error is noticed.
For instance, we would not consider a car dealership to be contractually bound to sell cars for $3000 a piece if a typo caused a zero to be left off the price in an advertisement. An advertisement or coupon simply does not constitute a contract.
In that same vein, I would argue that making an internet purchase is not a contract as well, or rather, at least not initially. Giving a company your credit information and clicking "Purchase" is not the same as handing another person cash and shaking hands, as that credit information must first be authorized and processed before money is actually transferred. Until that is done, the transaction (and hence, contract) has not been completed, and you the consumer aren't entitled to anything. Consequently, if an error is found at this stage, I see nothing wrong with a company cancelling the order in question.
If money is transferred, that is a whole different ball of wax. The deal is then done, and a business should be held to whatever price they stated. At that point they have taken your money, depriving you the use of it for anything else, and it is not acceptable for them to cancel the order simply because of their incompetence, anymore than they can call you up a month later and demand more money for an item you already purchased.