Like anything, it's all about balance
Whilst I couldn't agree more with your overall theme (that a policy of BYOD can be more of a cost and hassle than maintaining corporate devices), I don't think anyone advocates an 'all or nothing' approach.
Just as it would be crazy to expect people to supply their own high-powered graphical workstations (in the architecture or design industry), so too is it crazy to give people a corporate mobile phone when they have a perfectly good one of their own.
It's horses for courses. If I'm an architect or designer, I'd expect the company to supply me with the best tools to do my job as an architect or designer. In this case, it will be the latest high-power Apple machine or equivalent.
However, if I'm joining a company and I already own a perfectly good iPhone or Android, then why would I want a second device? Not only is this costly to the company (a 3 year TCO for a smartphone is £1,200 if you include the device, airtime, upgrade, replacement), but it's inconvenient for staff and costly for the environment (these precious metals in todays smartphone aren't without environmental cost). It's even worse if I'm an iPhone user and yet I'm given an Android phone for work (and vice versa), and stupider still if I'm an iPhone user and am given a second iPhone to make and receive work calls.
What's needed is a damn good solution which enables two numbers on one phone (one personal, one business), so I can make and receive calls for each number on the same device, but for work calls to be automatically charged to the company. In that way, I carry only one phone and yet came make or receive both work and personal calls with ease. One such service is BT smartnumbers, and I'm sure there are other like this.
So, while a blanket BYOD policy for tablets, laptops, workstations, phones etc doesn't make a lot of sense, it does make sense to target sections of these (such as smartphones) and crafting a BYOD policy just for these.