I believe the reason with all of those is the same, small parts can come off and become obstructed.
In addition greenies and nylabones aren't 100% digestible.
Hooves I hear stink badly after a chewing.
Some people still give rawhides, I rarely do with supervision, (choking).
Some dogs don't have problems with any of them.
I have an aggressive chewer so he gets bully sticks, the black kong stuffed with goodies, sterilized bones stuffed with goodies, and raw bones.
I gave him some pig ears and rawhide and he coughed up pieces a lot because he ate them so fast, so I don't anymore. No experience with other ears.
EDIT: I found this articles that I thought was interesting.
http://www.bizjournals.com/kansascit...06/daily9.html