I fail to see how visual aids detract from the art of storytelling.
It depends on what your goal with storytelling is. For example, if you feel that oral storytelling should rely on just the verbal communication tools to convey the story--encouraging the storyteller to become a better storyteller in skill--then visual aids detract by giving a concrete example. It makes you descriptively lazy. On the other hand, if you view RPing as entirely an entertainment passtime, you might not see developing your oral storytelling skills as any sort of priority, and most people don't. It's a difference in approach. All dependent on what your goal is.
But, if you recognize your goals, you will likely not slack just because you have visual aids... Although, personally, I've been storytelling for over two thirds of my lifespan, and on a medium like r20, I have trouble sitting and staring at the blank whitespace while telling a story. It's nice to have a visual. But its important to remember to describe the scenes fully... not to rely on that imagery. I suspect this is one of the reasons some folks have been asking for adjustable tokboxes that can be moved around, made bigger, etc, for those times when they don't have a handout or whiteboard stuff to display to their players.