At first, that was the case.

Then, Chase Bliss Audio pedals could interface with the Empress Midibox, though you need to flip the tip and ring for it to work.

Then Alexander Pedals got into the ring with Midibox compatibility. By ring I mean, the ring between the tip and the sleeve. Actually, I don't think Alexander Pedals do anything with the ring so forget I said that.

Then Distaster Area started making controllers with a Multi-jack output. This output has the capability to produce the same output as a Midibox.

Then Meris started making pedals that were compatible with the Midibox. All their pedals are compatible.

Now there's even a bunch of different Midiboxes on the market! Woo hoo! I'll 

Empress Midibox2 : the one that started it all! (well not really, I guess the midibox started it all). Also, the ugliest of all the midiboxes. Has midi return on the ring of output 1, for extra functionality. To use with Chase Bliss pedals, there are a couple of options:
1) You can buy the Disaster Area Designs MJ-CBA (MultiJack to Chase Bliss Audio) cable:

2) You have to do some soldering. Here is a link to a video by Chase Bliss outlining the process:

    Here is a photo of the PCB when you open up the Empress MIDIbox2 with clear modification instructions on        how to interface with Empress, CBA, and Meris pedals:


Chase Bliss Audio Midibox : internal jumpers to make it easy to use Chase Bliss or other pedals. No soldering required.

Meris MIDI I/O : Has wireless compatibility with bluetooth MIDI adapter?!? Crazy!

Disaster Area MIDIBox : also has internal jumpers.

Then the MIDI Association said to hell with current loops, let's just set a standard for DIN to TRS. And then went with the same thing that the Midibox uses!