What did I miss? Allow me to anwser my own question. A LOT, as expected.
I know the topic does not appear to be about Sakurai's arm pain right now, but here's something I forgot to say.
He might be spending so much time on the game because he fears what might happen if development of Smash 4 was haulted any further, a lot of people might get upset about it.
Of course, not everyone will know that Sakurai is in pain, and some people might not even care. Unless Sakurai is simply very dedicated to Smash Bros., fear over reactions from Smash Bros. fans is likely a major reason as to why he is spending so much time on the game.