I have never liked the idea of having to an "extra" step in order to receive a discount or OBC. I do believe that companies believe that a number of people will not do the extra step and the company keeps the money.
My rule of thumb: If instructions say you need to do something then do it. If you don't know how then talk to someone who can tell you how to jump through the hoop. The company sets the rules and if you don't follow them you are out of luck. Do I like it? Is it fair? No: But that's the way it is.