Anthony

In 2002 Zahi opened the tomb of Ny-Nsw-Wesert on the Giza plateau and made the comment that it had several features he identified with Khufu's chamber, including two unexplained exit holes which he likened to the upper shafts we have been discussing.
If they were open to the elments it might throw some weight behind Khufu's being left open to the elements. After all Ny-Nsw-Wesert's was a tomb. I really don't know the answer but it might be worth checking.