I can’t recall seeing a lot of Woody Allen movies where he appears glass-less. Do you find the refractions distracting? I find them part of his character.
My own WAG is that it’s a case of not realizing that people do notice that detail, and it being cheaper (but maybe not so much now) to put two pieces of window glass than one piece of zero-graduation glass in a frame. The frame itself obstructs the view of the face a lot more than the kind of curves you get on real glasses. I’ve heard actors talk about getting a role where the character wore glasses and just bringing their own, and people being terribly surprised “you wear glasses?” “well, usually I wear contacts, but I thought it would be silly to wear contacts under flat glasses… anyway, I have these three frames, which ones do you like best? Or should I get a different pair for the character?”
scifisam2009, I think that often writers don’t bother to define why does the character wear glasses. My mother is shortsighted and going on in years: she used to keep her glasses on all the time, but now they bother her when she’s got to look at something close up so she takes them off - in order to see better. I know many farsighted people who only put them on when they are looking at something up close (sewing, reading). People with astigmatism are likely to keep them on. How many people do you think have given this kind of tiny little detail any thought, even among those who wear glasses?