Rainchecks don't reserve systems. They are just a piece of paper that says what price you are allowed to get the thing for when they do get them back in stock. So if you come back and they are out of stock still you need to come back some other time.

I agree with you on the traditional definition of rain check, but the Wii issued rain checks last year and they were to reserve a future system at the normal price. I think that is what K-Mart meant in its add. It is communicating to people that they will not be allowed to reserve a system. 

I think it's hilarious that people think the 360 is having "horrible sales" right now. They are holding steady at good monthly sales, considering that their console has more market share than PS3 and they had no MGS4 type of games come out this summer. (Ninja Gaiden II hardly counts, even though I loved that game.) Not to mention that the PS3 isn't considered to be having great sales at the moment either. Unfortunately for both companies, the summer is not a good time to judge success, since it's a bad time of year in general for gaming. The real test will be the price cut coupled with the exclusives and other AAA titles that are coming out in the next few months.

As far as the rain check issue, I used to work at Best Buy and we would give two different types of rain checks. If there was an item on sale with a rebate and we ran out, we would give rain checks so that the customer could still take advantage of the rebate. If we just ran out of a normal item and people were asking for it, we would sometimes give them a raincheck and would call them when the item came in on a first come first served basis. Other times we would just tell them to check back for the item on a certain date.

In K Mart's case, it may just be that they don't want to get involved in all that.