I don't think it will make much difference defensively. Song was too busy trying to grab a goal than he was attempting to defend.
I thought he'd played well to be fair. If he's bombing on as much as he was, it's as much at Wenger's discretion as his own. It wasn't like Wenger had a go at him when he got forward, or hauled him off because he was disobeying orders. Song was clearly pushing on as he'd been asked to.
Not sure how Song can get sent off for an innocuous block in the opposition half, yet Bramble gets nothing for hacking Wilshere down when he's about to power into the penalty box?