That's an illusion mainly caused by how much time more high-ranking clones spend with the main characters (Jedi). Since they spend a lot more time on-screen, they're the clones we see the most and as such require names to easily identify them.
To a certain extent. Armour add-ons like shoulder pauldrons tended to be reserved only for commanders (though not all commanders wore them). Waist capes were primarily used by higher-ranking troopers but could also be seen on cold weather troopers and flame troopers.
All that being said, as the war progressed more and more clone troopers seem to individually customize their armour. However, it's been pretty inconsistent across the various canon mediums.