ditching jet with wide bypass engines

[lynn789]

for a long time the general wisdom was that the shear pins were partly there so the engines would break off on hitting the water to stop the engines digging in and destroying the plane

now it seems from the hudson river ditching that the jet has to touchdown tail first to keep the engines above the water as long as possible, and the shear pins most likely wont allow the engines to break off during ditching
howcome everyone seemed to have it wrong for so long?

is it now accepted that the shear pins are there only so a badly vibrating engine can fall from the wing