For a long time I have been trying to find a way to create a key shortcut natively in OS X to launch an application. It appears that there is a way to assign shortcuts to switch between already running applications, but nothing which allows you to assign a shortcut for a cold start of an app.
I think this is something which is very basic and Apple very much needs to hear your voice. You can leave a comment/suggestion on the official Apple OS X Feedback page.
Hopefully, aided with the help of people speaking up, we will see in the next version of OS X this very basic shortcut ability addressed.