Originally Posted by
Yaatri
Boeing 777 will have wingtip devices.
Not all of them. The newer models (773, 77L) have a raked wing design that provides similar benefit. The 77A and 772ER (the earlier 777 models) do not have the raked wingtips and can potentially benefit from winglets.
As for why they are less efficient at climb-out/landing it is an aerodynamics and speed thing. At the slower speeds the vortexes aren't as big a deal. At higher speed they are and that is why the winglets help at cruise. At least that is my understanding of it.