Comment 1 for bug 1367871

UAL isn't designed to run custom binaries how ever you'd like, it's designed to launch applications. An application is defined with a bunch of different metadata, but one of the key ones is a desktop file. That file defines how to launch the application and is what UAL decides to use for how to launch it. In this way the application can get launched in a consistent manner and is the same thing from device to device.