It's called Vanity Sizing.
Think your buying a pant with a 36" waist? Think again. At the Gap, it may say 36" on the label but the reality is that they are 39". At Docker, it's 39.5" and at Old Navy, it's 41".
But hey, you feel good about parting with your money for a 36" waist! If you had to walk a pair of 40" trousers up to the counter... Well, studies show that men will tend to walk away rather than admit publicly they are getting fat.
So, with vanity sizing, everyone's a winner. Right?