Still, it's probably just a sad set of coincidences. And very probably the smoking.
I think this is it really. With regard to asbestos it would be interesting to see what the wider situation was with regard to all BBC staff, not just companions; the camera men, lighting technicians, producers, directors, grips, cleaners....obviously a lot of companions and Doctors from that era are still alive and still healthy.
People die younger than the average every day, it's just more noticeable and harrowing to a wider audience because they're people we saw on the telly.