I think proactive communication (or proactivity in general) is indeed a major differentiator in level of service quality, and almost free for the company to provide - just requires somebody to care enough to implement these things.

If we're wishing upon a star, I would even go so far as to expect an automatic refund in these cases. The service bought was reserving a particular and specific seat. If said seat cannot be provided for whatever reason (whether BA's fault or not, whether within their control or not), the service has ultimately not been provided, and asking the customer to then spend more of their finite amount of time on Earth filling in forms to get their money back is adding insult to injury IMHO.