The MIDI to 3,5mm minijack adapter follows the Novation "standard"; at the time of the design there was no real standard defined (at least for my knowledge) so my choice was the Novation style. Interesting to hear there is an officlal MIDI spec now!
I was looking just the other day as I knew there were at least two standards (TRS MIDI A and TRS MIDI B) and, of course, I had equipment that used both standards, so a simple 3.5mm TRS lead wouldn't work.
I looked it up with the simple idea that I would just cut a lead and re-wire it, to save messing about with a 5-pin DIN lead in the middle. Also, because the adaptor that came with my AE Modular just doesn't seem to work any more (it's just a bit flakey).
Anyway, here's an interesting article that I now see makes note of the MMA Specification. The article has a useful table that shows what manufacturer uses what standard.