Unrelated to the article, but Marco & a couple others now run a different podcast: http://atp.fm/
For Gruber, I assume it was just money. Someone else offered him more or an ownership stake that he wasn't going to get from 5x5.
Siracusa and Arment both said they thought the shows had run the course. Siracusa is also a regular on The Incomparable [4].
[1]: http://5by5.tv/talkshow [2]: http://5by5.tv/hypercritical [3]: http://5by5.tv/buildanalyze [4]: http://5by5.tv/incomparable