I am a 777 pilot for UAL . The thing about winglets is this , they are only economical for long ranges , but I agree with you , I dont know why the B777 doesnt come with a winglet option , well maybe not just the 777-200 like i fly , but definately on the IGW or the ER's would be most appropriate. Also the B767-400 doesnt really have a "winglet" its more of a "wingtip" a true winglet , is what you would find on a MD-11 , B747-400 , A330 , A340. The B767-400 is a type of wingtip that Airbus uses for its A320 , A321 , A319 and soon on the A380 and the A318. Hope this answers your question!