For the eagle-eyed who noticed the tensorflow Arm wheel is not found on PyPI, it's actually on piwheels.org - a project I run which automates building all the Python packages on PyPI. In this case, the wheels were submitted to us from the TF team at Google. Raspbian is configured to use piwheels.org as an additional index so Raspberry Pi users get pre-built platform wheels just by typing "pip install".