The Ethics of Recasting: Audio Mistrust in The Archers

I have long been an avid listener of BBC Radio 4's epic farming soap opera The Archers. As I said on my post about 'Blindness and/on the Radio', what I love about spoken word radio is the way that it is automatically accessible to blind people. The Archers has to have audio description built into its plot lines so that characters' speech also fills in the details we cannot see: like a film's audio description soundtrack, The Archers' dialogue tells us who characters are with, what they are doing and where they are.
Just as (I imagine) sighted viewers recognise the characters in their favourite television soaps by their appearance, I recognise Archers characters by the sound of their voice. But recently, there has been a spate of re-castings on The Archers which leave me confused, disorientated and more than a little dissatisfied. Whilst television recastings are incredibly rare (Lucy in Neighbours, Miss Ellie in Dallas, and Sam Mitchell in Eastenders are the only examples I can think of in the last 40 years or so), at least four major Archers characters (Clarrie, Hayley, Tony and now Tom) have been recast in recent years.
I know there are always practical reasons for recasting and it is not a decision producers take lightly. But the expectation that listeners will quickly and easily accept a new audio incarnation of a beloved and long-standing character paradoxically undermines the importance of voice to the very medium which depends on it. Helen's effusive repetition of Tom's name is not enough to convince me that this interloper is in fact Tom Archer. Radio listeners - like blind people - know how to identify people by voice. This is a skill built on the assumption that people are who they sound like: radio drama can only function successfully if producers respect this assumption. When the sacred link between voice and character is broken by an unexplained voice change, the listener's trust in audio falters and The Archers loses some of its magic.