In Mongoid, are there any differences in the Date, Time, DateTime, and TimeWithZone field types?

The documentation mentions the four types of time related field types (http://mongoid.org/en/mongoid/docs/documents.html#fields). In other databases, I can see how these fields are going to be difference types in the database but for MongoDB aren't they all going to be Date types? Is this just for consistency with ActiveRecord?