The difference is that the distribution is not limited to that store. When the app distribution method is limited, this is what people wrongly call the "ecosystem" of an app store when in fact an ecosystem would actually be one where no limitation on distribution of apps exist; where sourceforge.net is a method of distribution, where a repo is a method of distribution, where email is a method of distribution. This diversity is what should be defined as an ecosystem. one apple tree which a handful of worms feed on is not much of an ecosystem.