Many golf irons have relatively straight leading/bottom edges. Hence golfers who are not of average height and proportions have to have them custom fitted or adjusted for lie angle. If the leading edge was a bit more curved from heel to toe, this would be less necessary, and the clubs would be easier to use from sidehill lies. After all fairway woods and hybrids with more curved bottom edges generally don't have to be lie adjusted. BTW I need my irons about 2 degrees flat lie. If I play with standard irons, I am quite prone to catching the heel of the club on the ground, which closes the face and therefore a lot of my shots will go left. Tall people may have the opposite problem of catching the toe on the ground and hitting shots right.