OT: how does software publishing work?

[Jonathon McKitrick]

When I used to look at the boxes all my games came in, there were always a
bunch of company names on it.  When I had an Amiga, Psygnosis was known for
always putting out good games.  However, the games often started: 'Psygnosis
presents... a XYZ game...'

Today I read that Valve, Inc. is hoping to deliver Half Life 2 to game
publisher Vivendi Universal Games.

How does the relationship work between writers and publishers of software?
If, for example, Psygnosis was known for high-quality graphics intensive
games, yet they were only the publishers, how were they able to find such a
continual supply of games that met their standards?

What 

jm
--