They could play attacking fields given the target was out of reach, so more boundaries allowed.
And i guess the point is that England is the home team and need to win to regain the ashes, so actually need to take a bit of risk!
That's the thing, they don't really need to take a crazy risk. They'll be extremely confident of winning the 3rd test with a rampart archer and no Smith/injured Smith which makes it 1-1 with 2 tests to go. No need to play high risk high reward in the 2nd test when you feel you are the better team (and they will feel that now)