pep-0492: Update Rationale section

pep-0492.txt

@@ -38,15 +38,15 @@ Current Python supports implementing coroutines via generators (PEP
 342), further enhanced by the ``yield from`` syntax introduced in PEP
 380. This approach has a number of shortcomings:
 
-* it is easy to confuse coroutines with regular generators, since they
-  share the same syntax; async libraries often attempt to alleviate
-  this by using decorators (e.g. ``@asyncio.coroutine`` [1]_);
+* It is easy to confuse coroutines with regular generators, since they
+  share the same syntax; this is especially true for new developers.
 
-* it is not possible to natively define a coroutine which has no
-  ``yield`` or  ``yield from`` statements, again requiring the use of
-  decorators to fix potential refactoring issues;
+* Whether or not a function is a coroutine is determined by a presence
+  of ``yield``  or ``yield from`` statements in its *body*, which can
+  lead to unobvious errors when such statements appear in or disappear
+  from function body during refactoring.
 
-* support for asynchronous calls is limited to expressions where
+* Support for asynchronous calls is limited to expressions where
   ``yield`` is allowed syntactically, limiting the usefulness of
   syntactic features, such as ``with`` and ``for`` statements.