And if you know the law of supply and demand then why would they not put the prices up. There might even be an interesting twist here in that the supply and demand in tension are time - do I buy everything in Tescos or shop around - the week before Christmas the answer to that is a no brainer!
Did they do anything illegal? No (unless the two were in cahoots which is illegal). Anything immoral? Only if you consider capitalism immoral (for which there may be an argument, but not one that many want to pursue). Was it not "right"? This perhaps is where there is some debate, but unless we think that they have a duty to do what is right by us rather than by themselves then No again.
There can perhaps be some debate about whether the action they have taken is best for them, but I haven't heard any complaints or suggestions that we should boycott them because of their behaviour - which suggests that they made the "right" call from their point of view. Of course this kind of decision can go wrong. The case of the Ford Pinto where Ford allegedly decided it was cheaper to pay compensation than fix a problem, but were then hit with punitive damages when this decision came to light shows the dangers.
Christian Aid update:
Wasted food costs the average family £420 a year. Give 42p for each type of food you binned this week.Mmm - well there were some old tomatoes, some stale bread and some sour milk - lets try 1.26.