Ah, it's the publisher discussion again. First of all I would love to know the title Chillingo asked for only 20% in shares? Hard to believe..a normal deal is about half/half (of course negotiable). From my experience with Secret Agents! for iOS and MacOS and Chillingo I'm sure this partnership did the game good. It's not only the name of the publisher, it's the entire QA process and their experience the game benefits from. Secret Agents! entire 2D artwork was done by Chillingo - and I really love what they did. I had to pay several tousand $$$ for this if I were on my own. So it's not only "hey, we have a big name so give about half of your money", there are "real" values behind a partnership like this. But of course every deal is different. Another important point is: Apple handles titles by well knows companies with priority in all these feature categories. I dont think there is any title by Chillingo that was not featured in any way. It's much harder if you are on your own. I would make it no different today.
A normal deal is more near 15-30%. Of course if they do some of your work ( art, programming ), they ask for more... They could also ask for more if they garantee you with a minimum sales( 50% but 50 000 sales minimum for example ). They could also ask more, if they are one of the bigest publisher, and that you are sure to have a good marketing cover. But a usual deal is near 15%-30% EA bought Chillingo, and not angry bird. Angry bird is a good product, but chilligo made it a success. So yeah Publisher are important.
The percentage rate should really depend on how much involvement the publisher has. Some will just take a finished game, release it and market it. Some will be much more involved in the production, helping with game balancing and design, QA testing, providing financial advances, and releasing and marketing. The latter are going to want a much larger cut, because they have committed time and money themselves before the game goes on sale.
