Re: This is where the cloud comes in?
You are fogetting a few things...
With BYOD, they still need to ensure the devices are physically secure - or as secure as they can be. For a mobile device, that means that they have to implement policies to ensure that any device which holds or caches corporate data can be remotely wiped (that means that your phone will report to the corporate "find my phone" equivalent, not your private one), that a security code has to be entered to unlock the screen before use, that devices aren't jailbroken (and thus bypassing some security), that they have the latest patches installed etc.
Those are things many users won't want the company to do to their devices.
Additionally, phones and tablets, which are single user devices, would not be usable by your kids/spouse friends etc. once they had been attached to the corporate network - data protection guidelines.
For home computers, it is a little easier, you have to ensure that the account which can connect to the corporate network is secured and cannot be accessed by other family members - and that means that other family members don't get admin access to the machine either.
Additionally, they need to ensure that the machines have active malware protection suites installed and that they are updated.
All of that can be done using corporate management tools, if the machines are owned the company / council. For private devices, that configuration and checking will often have to be done on a device-by-device basis, which takes a lot longer than hitting the send policy button.
If it comes out that your spouse is regularly using your iPad, which also has corporate applets on it, which pull financial details or personal details about customers (names, addresses, telephone numbers etc.), then the company could be liable to fines from the ICO.
That is all a huge headache and extra costs in time managing the devices, which many don't take into account when they hear BYOD. They think they are saving on the device purchase cost, they are; but those costs probably amount to under 10% of the total cost of the device to the company over its lifetime. And if those other costs escalate, due to the device being "different" to the corporate standard, the cost of BYOD can easily be much higher than providing employees with devices in the first place.
That is why it is critically important to look at the secondary benefits - happier workforce, more flexibility etc. to see if they outweigh the additional costs of BYOD.