Yes, I'd go as far to say as most top level refs are good speakers.Think it is more that they aren't allowed to. We've heard most of the SG1 referees talk at events, conferences, or with Mike Dean even on the Peter Crouch podcast, so I don't think there is an ability problem, it is just not allowed.
Every event I have been to where there has been a key speaker (Dean, Coote, stroud, Kavanagh, Taylor) all speak really well..
Being able to. Communicate is a key skill to be a ref.
Communicate with players
Communicate with team
Communicate with managers
Communicate with observers (this being one of the most important, if you can spin the observer he is going to mark you maybe better than he orignally planned).