Even if it didn't have any apps, it provides complete and open access to the Internet for $25 to people who might not otherwise have access to it. Wikipedia, email services, OpenStreetMap, Twitter, news sites, political forums, MOOCs. It's a chance to give the last billion people their voice on the open Internet.
Next billion, not last billion. http://www.internetworldstats.com/stats.htm says that of the 7 billion people in the world, just shy of 2.5 billion have internet access. http://www.internetlivestats.com/internet-users/ claims 3 billion. http://en.wikipedia.org/wiki/Global_Internet_usage claims about 3 billion.
All of which is to say that less than half the world actually has anything like consistent internet access today. And yes, getting those next 4 billion people on the internet is one of the explicit goals here.
If there's no way to do something similar on Firefox OS, then I see that as a much worse hindrance to the ecosystem than the income demographic they are targeting.
He's already submitted a git browser: https://marketplace.firefox.com/app/git-browser
This generally means that targeting the lowest end of the market isn't a great idea unless you are trying to make money off the sale of the device alone and not ongoing services like apps.