Yes they did? When you buy a product you implicitly agree to certain common law rules regarding that product - in this case, rules around intellectual property. You can't walk into a restaurant, order a nice meal, eat it, and then say "hey I never signed a contract that said I would pay for this meal".
Not only that, a lot of the time it is explicitly specified - load up a (non-pirated) DVD and the first minute of your time will be spent being reminded of basic copyright law and penalties for breaking it.