elementary OS isn’t just a community. It’s a culture. And this culture has its own conventions; its own way of doing things.
Not all open source projects enjoy the kind of following that elementary does. While people do make apps for GNOME or KDE, have you ever heard third-party devs writing something for one specific distro? Like say, an app targeted for Mint or Mageia? No. But there is a whole community of developers who are building apps solely for elementary OS. Most of them don’t care if their app even works on Ubuntu, Debian or any other distro. All they care about is following the elementary HIG, and making life easier for elementary users.
It’s because elementary OS is not just another Ubuntu fork. It has a philosophy. A purpose. It is a way of life. And people who share their beliefs about usability and simplicity, are bound to join the culture and enhance it further.
If you like an easy, clean and clutter-free OS, I strongly recommend elementary OS.
Talking about elementary-focused apps, there’s this PPA that hosts some of those. It contains all sorts of commonly used apps like feed readers, microblogging clients, productivity apps and what not. All for the love of elementary.
Most of them are still unstable and/or incomplete, but it won’t be long before they’re finished. It’s always easier to develop for elementary OS, since there’s so less to care about if you adhere to their guidelines.