Yes but they can be part of multiple preset. 

The point of having a callback 'name' is that user can just say : 
Oh, I want those 3 button from Slideshow mode and this one from ChronicleLabs plugin. 
I absolutely don't want them to mess with javascript. 

so `register_preset('my preset', ['slideshow.foo', 'slideshow.bar', 'slideshow.qux', 'chronicle.awsomeness'])` stand by itself.

also this allows to register "anonymous" callback and use them in a few places where passing references would be really painfull. 

Lastly you could build a list of availlable callback if needed, which are named, 
wherease in your example user would have to chose between `function(cell, meta){...}`, `function(c,m){...}` ...