You'll just have to believe me, Redwood.
Where I live, I've never seen a screw-on tub spout with a hole in the bottom to provide access to a non-existant set screw.
What you have there is a company that's simply using the same cover on their screw-on tub spouts as they do on their slip-on tub spouts, and I don't think that's a good practice. If a home owner sees a hole to access a set screw, but doesn't find a set screw, he's going to be reluctant to conclude there isn't a set screw. Instead, he's going to wonder (as you suggested in an earlier post) if the set screw has rotated on a collar and is no longer visible from the bottom.