The risk of losing data is too high for someone in such an important position.
Hell, even 10.3.0 corrupted your data if you turned file vault on. So release candidate, and even final releases mean nothing!![]()
I would expect Steve Jobs to use beta leopard day to day, but guaranteed he will have many many forms of backups (a couple of MBP's probably). He seems too hands on to not provide feedback throughout development process on what is arguably the most important piece of Mac software.