Simply put, there's more margin for error. The size of the clubs allows designers a lot more freedom than they have while designing irons. Adams Golf helped popularize a low-profile concept with the Tight Lies fairway woods. The majority of the hitting surface is in the bottom of the face, where the club makes contact with the ball. That's why robot testing is so misleading.
Robots only make solid hits.
Adams points out that irons are face-weighted, while fairway woods have an extremely low center of gravity. An iron and a comparable wood may have the same degree of loft, but the wood will almost always go higher because of the low center of gravity. The fact that the shaft on the wood is a couple of inches longer also means players can generate more clubhead speed, producing more distance and height. Irons are flat, while the curved face of many fairway woods can produce a gear effect that brings toe and heel hits back toward the center. Utility clubs also have a wide sole, which means they will cut through thicker grass easier than a long iron.