I don't know about Automattic, but in many larger companies, super-stars-with-nothing-to-prove go through different hiring experiences than most other employees. I can't imagine Google or Dropbox sat Guido Van Rossum in a room and asked him to reverse a linked list in 'whichever language he was most comfortable in'. Although I might be wrong, of course... ;)

For people who have something to prove, well, the only question is which particular strategy the company will use to ask them to prove it. As far as it goes, 20 hrs of paid labor outside of work if your contract allows it, is not the worst I can think of.