db.ReferenceProperty() vs ndb.KeyProperty in App Engine

ReferenceProperty was very helpful in handling references between two modules. Fox example:

class UserProf(db.Model):
    name = db.StringProperty(required=True)

class Team(db.Model):
    manager_name = db.ReferenceProperty(UserProf, collection_name='teams')
    name = db.StringProperty(required=True)

• To get 'manager_name' with team instance, we use team_ins.manager_name.
• To get 'teams' which are managed by particular user instance, we use user_instance.teams and iterate over.

Doesn't it look easy and understandable?

In doing same thing using NDB, we have to modify

db.ReferenceProperty(UserProf, collection_name='teams') --> ndb.KeyProperty(kind=UserProf)

• team_ins.manager_name.get() would give you manager name

• To get all team which are manger by particular user, we have to do

  for team in Team.query(Team.manager_name == user_ins.key): 
      print "team  name:", team.name
  

As you can see handling these kind of scenarios looks easier and readable in db than ndb.

• What is the reason for removing ReferenceProperty in ndb?
• Even db's query user_instance.teams would have doing the same thing as it is done in ndb's for loop. But in ndb, we are explicitly mentioning using for loop.
• What is happening behind the scenes when we do user_instance.teams?

Thanks in advance..