Does mobile gaming still need publishers?

Every game needs a publisher, whether you do it yourself or hire another company for that role. Publishing is a skilled task, a necessary step for any game to find success. But what criteria determine whether a developer needs an external publishing partner (someone to finance, market, and distribute their game), or not?

It has never been easier to self-publish via the App Store or Google Play, but uploading your app is just the beginning. What about the marketing and PR savvy, media contacts, social media skills, and customer response utility needed to acquire and retain thousands (or millions) of users globally with proper localisation?