Filter Size: Manufacturers tended to stay with standardized filter sizes. Pentax chose 49mm. Nikon chose 52mm. This was important because black and white photographers often carried several colored filters to alter the appearance of their images. Red filters was chosen to darken skies but would also affect facial coloration. Yellow filters darkened skies less dramatically without altering complexions. Orange filters were available as a compromise. Green filters improved foliage in landscapes. Add to these three basic filters a polarizer and a soft focus filter or two, and you could have a sizable amount of money tied up in colored glass disks. Today, software can approximate the effects of colored filters, so photographers are no longer carrying stacks of filters. And if I remember correctly, filters were much more expensive in relative dollars in those days.
Focus Ring Rotation: This could be really important to speed shooters. Probably nothing worse than trying to focus on an inbound subject and having the background snap into sharp focus. Autofocusing lenses pretty much make this a moot point.
Nikon Lenses: When viewed from above, nearly all Nikon lenses have zoom rings have the shortest focal length on the right and the longest on the left.* This also appears to be the case with Tokina and Tamron lenses. Current production Sigma lenses appear to rotate in the opposite direction, although there are examples from these three manufacturers where these rules don't apply. While I can't make a broad statment that is 100% accurate, I suggest that before buying any lens from any manufacturer, check to see the direction of the zoom ring.
Fortunately, all my working lenses are Nikon oriented, except for the big Sigma, which comes out occasionally to make a special shot. And yes, the oposing zoom rotation does trip me up from time to time. So for the most part, this lens and I just try to get along.
*There is some notable execeptions such as the early, non VR releases of the 24-120mm zoom lens, and some older zooms that pre-date the digital age. The 28-200mm Nikkor also has the reversed zoom ring.