As it was mentioned somewhere before, Chrome 45 does not see some MIDI ports, including the Microsoft Wavetable Synth.
So, if you don't have any external MIDI devices connected, Chrome's Web MIDI Api will see nothing.
I don't know what reason was behind the Google's decision about that. The result is the same whether or not you are using JZZ.js.
jazz-midi extension fixes the situation, and that's why it's still useful even with the Web MIDI Api around.