OK...well if you buy an air mattress and it is loosing air I wouldn't have the reaction "Oh no this is not happening!"...it seems like you are being over dramatic....if a company makes 100 Million of those things in a year a few are bound to have leaks....come on get real. I myself have owned probably 6 or 7 different air mattresses from wal-mart....I have used them for everything from road trips to pool toys, and they have all been great. In fact the one we used as a pool toy we had a contest to see if anyone COULD pop it by diving into it and nobody could.....so I completely reject your categoric statment that the matresses are "junk" you just happened to get a bad one. I have had many that have held up under suprisingly rough treatment.
As far as the policy goes, it is fair. Air Mattresses are basicaly expensive balloons, and of course they are prone to popping. And most people only need them for one or two nights. It is the kind of thing that would get returned ALL THE TIME if there wasn't a policy on that. Who would really "buy" one when you could just get one, sleep on it for a few nights, and return it when you were ready to go back home. The policy is in place for a reason.
As far as the policy not being displayed....well the policy IS displayed at the customer service desk as a general rule...but in a place like wal-mart...where they sell EVERYTHING....there will be different policies for housewares, electronics, potting soil, food, ect. ect. ect......it is not the job of the store to wall-paper their isles with big giants signs that explain everything....it is YOUR job to be an informed consumer and ask.
And if you REALLY needed another mattress....then what was so bad about them offering you an exchange....it sounds to me like you are just being a jerk.