Well, there are definitely a bunch of things in Shakespeare plays that are subtle and contextual to the times enough that we've actually lost the sense of their vulgarity as well [1]. The common perception of Shakespeare as exclusively high-brow, when in reality it played to both an upper and lower class audience and that was probably a part of its appeal, does seem to be reinforced by the way it's taught in school.

[1] An example: http://en.wikipedia.org/wiki/Much_Ado_About_Nothing#Noting