In my opinion, the most important contribution (by far) of bitcoin is that it enables true 2 party transactions to occur over the internet. That has profound social implications and might be something that the TED crowd would would be interested in hearing about. The fact that bitcoin isn't issued by a central authority is of secondary importance.
This is TED. The problem isn't "promotion", it is that you are trying to promote the wrong thing.
Try rewriting it in the language of
self-promotion. You explain the social implications, but the subtext needs to be that you are totally awesome because you understand this cool new thing, and by extension the audience will be much cooler than all of the dumb proles out there because now they know it too.
And before anyone flames me, go watch a few talks.