I'm pretty sure some of the magical logic in Portage was supposed to make sure it calls the currently used interpreter directly rather than relying on /usr/bin/python working. However, I just got an issue where broken /usr/bin/python has caused internal portage helpers to fail hard and brick Portage for me. I'm going to investigate more.
Oh, nevermind. Just noticed it was due to python executable rename from python3.4m to python3.4.