I guess it depends on what WalMart you go to. I brought mine to the one near me one evening, and I was the only customer they had (it was just before Christmas). They must have been bored looking for something to do, because they jumped at the chance to work on my Jeep to rebalance the tires (285/75/16") that I did not purchase there. They also must have rechecked the torque on the lugnuts at least twice (they told me they do it a couple of times to make sure someone doesn't drive off and then complain their wheels fell off) before I left.
And they sell 33" tires at WalMart, so I don't know why they would tell someone they don't have enough air pressure to air up 33" tires. Maybe someone was lazy there and just didn't want to work that day.
By the way... I love the smell of new tires.