LG wrote: I think it's just a fact that we're getting older.
Indeedy. They were all in their late sixties (save for Lemmy who was a couple of days over 70 and probably helped himself on his way out following his diagnosis, I suspect) and three of them had cancer. Frey died of "complications arising from rheumatoid arthritis, colitis and pneumonia" (Jeez!) and Buffin had Alzheimer's
That's probably just a fairly average sample of those who die in their late sixties, sad to say. They just happen to have been famous to varying degrees and to have died in a little cluster, at least from our narrow point of view. (I doubt that many under 50 who are mourning the loss of Bowie, Lemmy or Frey will have much of a clue who Buffin was, or Rickman aside from his Snape role.)