Maybe, when they say "leg", they mean that SYD-OOL-SYD is one leg, i.e a return trip. Fitting 8 SYD-OOLs into a day would be pretty tight. Or, maybe because Jetstar will operate a lot of longer sectors (2-3 hours, not really long I know!!!), such as SYD-TSV,HTI etc, that 4 of these legs will make a tight schedule also. But, at the end of the day, each aircraft won't operate the same number of legs, as depanding on the length of the routes each aircraft fly, some will do more than others. 4 must be an average figure.
I think though that the big surprise and interest is not where Jetstar fly (except for the new routes that have never been flown by an Australian airline before), but what changes will occur with QF mainline. Will mainline resume flights on HBA-MEL, BNE-ROK etc (which apparantly get a lot of suits on board and plenty of full Y fares) or will these ports be just served by Jetstar? End of Feb ain't too far away.