All app stores, IMHO, are about app discovery for people who want to search as little as possible. The iPhone app store is the only way to get apps "legally" on the iPhone, but other than that, app stores don't do a whole lot other than search. Android apps can be sideloaded, Mac store apps won't be anything new, and Chrome apps aren't either.
Having a button for the average user to press is what it's all about. "Press this button, and you can find apps." It just serves as a way for people to most quickly find something that meets their needs. For developers, it gives those people a place to look and hopefully increases exposure.