There are many differences between the classic physique and the over-developed, chemically-enhanced "Hulk"-like physiques of today. An important difference is in leg shape and proportion.
Look at the photos above. Leg shape in the classic physique (above photo: left) is what Vince Gironda - the Iron Guru - calls "straight." In other words, there is not much of a difference in measurement between the upper and middle thigh. Leg shape in the "Hulk"-like physiques of today (e.g., above photo: right) are what he calls "turnip-shaped" or "carrot-shaped." In other words, the upper thigh is much larger than the middle thigh, giving the thigh the shape of a carrot or turnip.
In the"Hulk"-like physique, overdevelopment of the thigh (specifically the adductors and lateral aspect of the quads) makes the calves look proportionately smaller thus destroying the balance between the thigh and lower leg. In the classic physique, the straight, properly developed thigh does not dwarf the calves, so that the flare of the calves is more prominent and adds more to the attractiveness of the physique.
In the above photo, take a look at the classic physique on the left (Steve Reeves, Mr. Universe 1950) and compare it to the "Hulk"-like physique on the right (Jay Cutler, Mr. Olympia 2006) in terms of leg shape and proportion. Which do you think is more attractive?