This appears to be Python 3 specific. On 2.7.4 (Win7):
>>> import sys
>>> sys.stdin='abd'
>>>

With fresh 3.4 repository debug build, prompt never appears, ^C, ^D are ignored. Must close with window's [X] button. With fresh 3.3, get repeated [62312 refs] lines. One could guess that they are generated but suppressed in 3.4.

There is a possibility that this is specific to debug builds; I cannot currently build or run one for 2.7. However, there is no problem with Idle running (on Windows) with 3.3/3.4 pythonw-d. (In other words, see same behavior as 2.7 above.)

Indeed, in both 3.3.0 non-debug and 3.4 tip debug, python starts consuming 100% of the CPU.  I'm guessing there is some subtlety involving the new IO system involved here.

Python 2.7 debug build acts as you indicate for your 2.7 non-debug build.

All my tests are on linux, and I had to kill -HUP the python process.  As you say, ctl-C (and ctl-D, not surprisingly) were ignored.

In searching for an existing issue about this, there seemed to be other edge-case stdin problems. I don't think that they were all usage errors. This problem was revealed by an accidental usage error that should have lain dormant until an exception was raised upon first use by input() (as happened in 2.7).

New changeset 68d1ac152b5d by Benjamin Peterson in branch '3.3':
ignore errors when trying to fetch sys.stdin.encoding (closes #17863)
http://hg.python.org/cpython/rev/68d1ac152b5d

New changeset 97522b189c79 by Benjamin Peterson in branch 'default':
merge 3.3 (#17863)
http://hg.python.org/cpython/rev/97522b189c79