I assume that now (meaning when you pair your watch, you won't see it until then...), it will show apps that have a watch extension from the App Store. Later, it will show apps that are 'watch local'.
There aren't any apps now that are anything except iPhone dependent with an extension. You choose which ones appear on the watch, of course.
You choose which ones you want on the watch in the watch app.
All that's what I understand.... anyone have anything to add?