Mark Houlsby wrote:

It's probably quite random. There appears to be no indication that the
players
who produced these statistics are particularly strong. We weak players
make random moves, and don't have much of a clue about strategy or
tactics.

I agree. It would be interesting to compare the results above with
another set obtained in a "computer vs computer" long match, assuming
then "perfect play". However, from the results in that table perhaps
one might conclude that "weak" or "average" players are more
conservative with their bishops (B) than with their knights (N), e.g.
you would rather exchange or sacrifice Ns than Bs. The table above
points out that the stronger the piece is (in terms of the player's
view), the higher its "live expectancy". As a matter of fact, I think
that the "captures" column above is the only one which somehow
correlates well with the theoretical strength of each piece (I don not
know how experts evaluate that). So yes, maybe it is random, but then
it is also "real life chess". Or just nonsense.