I grew up in a day when the vast majority of
binoculars were covered in leather or "leatherette". Tells you how old I am, I guess. Leatherette just spelled binocular to me, as it was something not found to any extent on other optical instruments.
Armoring on binoculars were actually quite rare when I was young - armored binoculars with rubber coverings didn't appear in any great numbers until the 70s and 80s. Today, of course,
armored binoculars rule the binocular roost. If you want a leather covered binocular with that "old time" look and feel, your options are quite limited. You still get that old leatherette on some
astronomy binoculars, but it is very rare on smaller binoculars. Guess that's why I had to grab a
Leica 10x25 BL, the L denoting a leather cover. Naturally, the L version also comes with a leather case.