Something like 80% of games are lead on the 360. It often makes more sense to make the 360 the lead platform because publishers and developers know that is where the most money is and the 360 tools are generally easier to develop with initially.
With multiplatform games, the 360 versions historically outsell the PS3 by a factor of more than 2. In fact, for many third party publishers, one single 360 title will outsell all their PS3 titles combined. This is due to the larger install base and the much higher attach rates.
btw - does anyone know how it works? you build a prototype game, show it to some publishers and whoever's interested you sit down with and talk about contract conditions (unless you're already under contract, obviously)?
That's is one way it can be done, but most developers don't work like that unless they are just starting out and trying to make a name for themselves. Unless a developer is being funded by a publisher, making a game is a very expensive and risky proposition.
Most often a publisher will hire a developer to make a specific IP that they own (or have licensed). It is fairly rare for a developer to actually own the IP rights of the games they are making.
