I think that the scheme previous years was that Hewitt's half always started second, presumably to let his round 3 be on saturday.
It's also the case this year, whereas I thought it would be Tomic's half instead of Hewitt's.
Wimbledon is the only tournament where it depends on the defending champion. In US Open, it seems depending on Roddick (first half, also to play his R3 on saturday, as in US Open first round is in 3 days), in French Open it's tougher to know, although Tsonga's half started first last two years (Tsonga playing on first sunday)
Yeh, I too thought the choice for Saturday play would have gone to Tomic instead of Hewitt this year