I don't recall why either. :) I spent today thinking about how easy
it would be to implement (I haven't taken a look at the code on the
Windows side but it sounds quite easy). Perhaps maybe I was thinking
of a different system of hints to the user--i.e. instead of automatically
appending ".abw" to any file that doesn't already end in it, it could
append ".abw" to just the file name entry box in the dialog whenever
the user chooses a file type from the types drop-down. The user
can then erase the extension; this is what Gimp does, and it's file
open/save boxes have that type drop-down in common with ours.
As long as its consistent it doesn't bother me. The Gimp dialog always
changes only the entry box and uses that string for the filename.
It never adds anything you didn't see first.
-- Shaw Terwilliger