Sony really wants to attract developers to its mobile platforms, and the best way to do that is by "removing any existing barriers" to entry. Sony realized that one major barrier could be the cost of publishing. The company had a policy to charge $99 for a license to publish on any PlayStation Mobile enabled device and the PS Vita, but that is gone now.
As of Tuesday, Sony has killed the publishing fee, so developers can now publish games for free. Whether or not this changes things for Sony remains to be seen, because both Apple and Microsoft charge a $99 annual fee to developers wanting to publish in either the iOS or Windows Phone app stores, and both stores have solid catalogs of games.