The winglets on the 757 are an after market mod, bit like go faster stripes only in the case of the 757 they are go further winglets!!!!
"Although production has ceased for the 757, blended winglets are now available from Aviation Partners Inc. as a retrofit to increase fuel efficiency and range. American Airlines, Continental Airlines, and Icelandair have commenced fitting them to some of their fleets, targeted at longer range routes which are too far for 737 or MD-80 aircraft but not popular enough to operate a B767 or A330"