The way you select a save slot in Zelda 1 is by pressing SELECT on the controller, and it only moves the cursor down.
The fact that I can select a save slot in Zelda Classic by pressing UP or DOWN on the control pad is good as these did not do anything at the -SELECT- screen in Zelda 1, and they are the first buttons many people try to use to navigate.
But not being able also use SELECT in Zelda Classic to do this, I think, is bad. A goal of Zelda Classic is to behave like Zelda 1, and people who have played that game on the NES (or virtual console even) have a lot of muscle memory. I was surprised that SELECT does nothing at that screen in Zelda Classic. It's just one more snag, and if a newbie hits too many snags they'll give up.
Why not allow both ways of navigating? The only advantage the current behavior has that I can think of is that it forces people to learn that they can use the control pad to go in both directions. I could envision someone who is used to the Zelda 1 behavior accidentally going into elimination mode because they didn't expect UP and DOWN to do anything, but I think that's unlikely if their thumb is on SELECT (and we can always add a confirmation step before deleting).