It is easy for Rovio to say they do not need a publisher: they are allergy a household name.
Truth is, Angry Birds is popular due to some very smart moves by Rovio. Today those same moves would not work, but in the infancy of iOS App Store, Angry Birds was no huge success. The combined downloads of the free and paid versions did sum up some high numbers though. So a few mohts later Rovio did what Apple wanted: they released numbers that looked impressive and portrayed the App Store as a place of success. They said the game had been downloaded half a million times (that was a cumulative of free and paid downloads, if I’m not mistaken.)
This was not rare at the time, but people used to be tight-lipped about their numbers. The press was starving for such hits and they ate the story extremely fast. Overnight, Angry Birds got huge press coverage all over the tech and gaming press and gained insane amount of attention. This combined with the game actually being rather polished resulted in the hit it is today.
By now, they no longer need the push, so it is true: Rovio needs no more publishing help in the mobile space. But the above is what a publisher does: they do their best to push your title into the spotlight. They invest money on getting you press coverage and advertise you, all this for a cut of your profits.
What should you expect from a publisher?
*You should expect them to promote you.
*You should expect them to get review sites to look at you.
*You should expect them (although not to succeed) to try to get you a spotlight.
*QA testing.
*Feedback on product quality.
What the publisher expects from you (this may vary from publisher to publisher):
*Integration with any social network the publisher owns.
*A cut of your profits (expect between 40% and 60% going to them after Apple gets its cut, percentage will vary based on sale numbers, how far into the publishing you are and your own negotiation skills)
*Full app store control (you won’t set prices, they will, it will be under their iTunes account not yours)
*Exclusive distribution rights for mobile for the next 5 years (for the entire IP, sequels and spinoffs included) They may also want Mac/PC rights.
*You to listen to the feedback they give (if you refuse to fix stuff they think is too bad, expect the deal to fall apart, depending on contract you may be legally bound to do the changes.)
Not all these things apply to all publishers, but it is the mixture of things that I got when I was asking around.
Mind you: you are not hiring publishers. They pick you. This means you can bring your product to them, and they may like it enough to pick it, but just because you look for a publisher does not mean you will find one that is willing to pick up your product. Easiest way to be picked would be going to a game convention. Decent publishers send representatives to all the decent sized ones, even the ones the press does not cover highly. They are there precisely hunting for potential. Contacting them directly may work, but the effort of getting to a con will carry a bit of weight (besides, the guys at the cons are in hunting mode, the guys at the other side of an email account are in fending mode trying to disregard all the junk mail they get.)