I agree to dired-do-shell-command's suggestion, but the line remains

[Dan Jacobson]

It asks me and I agree with RET,
(dired-do-shell-command "bunzip2" nil (quote ("file.bz2")))
but afterwards that line in dired is not refreshed to show the newly
unzipped file. Same with
(dired-do-shell-command "gunzip -q" nil (quote ("file.gz")))

Ok, indeed not simple for the general case, but the user is left
staring at the old file and must hit g himself.

dired-do-compress doesn't have this problem.