Explain in the "Data Model" document why arguments to __init__ are ok when __new__ is not defined

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-11-12.05:50:12.182>
labels = ['type-feature', 'docs']
title = 'Explain in the "Data Model" document why arguments to __init__ are ok when __new__ is not defined'
updated_at = <Date 2016-11-12.05:50:12.182>
user = 'https://github.com/jsbueno'

bugs.python.org fields:

activity = <Date 2016-11-12.05:50:12.182>
actor = 'jsbueno'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2016-11-12.05:50:12.182>
creator = 'jsbueno'
dependencies = []
files = []
hgrepos = []
issue_num = 28672
keywords = []
message_count = 1.0
messages = ['280633']
nosy_count = 2.0
nosy_names = ['jsbueno', 'docs@python']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue28672'
versions = ['Python 3.6']