Some random thoughts:

• A ban on crypto-exchanges on Chinese mainland is indirectly a blow to Chinese miners, as it will be harder for them to convert bitcoins to yuan, which is needed to pay for electricity, salaries and misc.
• The target for the ban is probably Chinese population (and Chinese institutional investors) - moving the exchange overseas will make it harder for the target group to trade crypto-currencies for fiat (as the banks most likely will block the Chinese from moving their yuans to/from the exchanges).