Where did the second parties go?

We were chatting at lunch the other day about 3rd parties building solutions on the audio engine.

One of the people in my group asked "Why do we call them 3rd parties?"

 

It's one of those "things that make you go hmm".

There's general consensus in the business world that the people/companies who build a platform are first party developers (it doesn't matter if the platform is Windows, Photoshop, or Quake III).

There's also general consensus that the people who build solutions ON those platforms (so applications on Windows, Photoshop Plugins on Photoshop, <pick your favorite game> on the Quake III engine) are called 3rd party developers.

So we've covered 1st and 3rd party developers, what about the 2nd party developers?

Wikipedia's definition for 3rd party developers is consistent with mine, but they describe 2nd party developers as developers operating under contract to 1st party developers -but they also say it's not a part of standard business practices.

 

So my question is: "Whatever happened to the second party developers?  Where did they go?"

Bonus question: From Microsoft's perspective, Adobe is a 3rd party developer, even though they build a platform.  If I'm a developer working on a Photoshop plugin, am I 4th party developer from the eyes of Microsoft?