I've done similar things with women's clothing. Gap/Old Navy are by far one of the most 'generous' with the concept of ease, especially in what they consider to be plus sizes (anything over a 12, from what I can tell). Any good tailor will put an inch or so of ease into a garment. It is as the term implies, a bit of room to keep your garment from tearing when you move around. What's even more interesting is how women's sizes are scaled. Between the smaller sizes, the measurements go up half an inch to an inch. When you get to the larger sizes, where the waist is above 28", the delta between the sizes can be as much as four inches. To wit, if you are small, then you get more choice in how much ease you prefer. If you are larger, you get either too tight or too loose.

So it doesn't surprise me that there's "vanity sizing" in men's trousers. Not even a little bit. This, too, makes for a tough call when it comes to getting dressed. Camel toe or saggy butt? Hm.

(eta: sorry for devolving this discussion into a rant on ready to wear clothing)