As mentionned by Gian Piero in http://bugs.darcs.net/msg19857 :
Explicit dependencies [are] still not included in the output of `log
--machine` as it is currently broken (displays the `--verbose` output
instead of the `--summary` one). Btw, `log --xml --verbose` is also
broken as it displays the same output as `--summary`. Not sure anyway
about what the correct output should be.