How the hell is is that Lucas made such a masterpeice that is "A New Hope" and yet when he directed his other 3 films they totally blowed? How did that happen? Because ANH is reguarded in the highest of light world 'round.
And back on the posters. The original poster look has that romantisism about it. Look at Vader in ESB. He's wearing some type of poncho thing blowing in the wind. There is action, adventure, intrigue in every corner of the poster. Luke, honorably gazing off in to some distant battle. Leia caught in the middle of danger.
The copied version? Ehh...not so much. Vader is (as someone so elequently put it) looming for that last doughnut on the confrence table. Lando is looking at you wondering what the hell that is on your face, and Luke can't believe that the Rebels left without him as he watches them fly away.