Attacker loses 45*0.7 = 31.5, which got rounded down to 31.
It is weird, it is usually rounded up.
For example, here, on Turn 4:http://warlight.net/MultiPlayer?GameID=5176815
Hitting into 5 results in 4 attacking armies dead. Every time I've seen a hit like this, the loss is rounded up.
Interesting settings. At first glance, seems that players can force a stalemate. But then it becomes less obvious.