What is the difference between an entity in Drupal 7 and a content entity in Drupal 8? The Drupal Examples "entity" project was really helpful for me when I was learning the entity API in Drupal 7. I have seen no explanation though for why this doesn't exist in Drupal 8 or why it was renamed, etc.
I'm not sure what you are asking.

Example modules are named after what they're an example of, it's not for them to pick a name, really.

Drupal 8 has Content Entities, which evolved from the field structure of Drupal 7's entities and Config Entities, which are based on concepts from ctools exportables, entity.module's exportable entities and various other things.

Both share the same base class and a few comments and concepts but beyond that, they're quite different. Both are typed classes, Content entities have a strict although somewhat complex structure but are very extensible within that structure (That is, Entity -> Field Item List > Field Item > Property). They can have revisions and translations which are conceptually similar to field translations in 7.x but have a different API.

While there isn't that much documentation yet, https://www.drupal.org/developing/api/entity has some, there are also plenty of presentions from DrupalCons and other events about the concepts, API's and so on, including a recent one that I co-presented: https://2015.drupalcamp.at/session/entities-drupal-8.