Why stop there?
Once you've got peole to accept that they must spend the money you pay them to buy a device to do their work on, the possibility to take this idea further opens up. First up you could try BYOS (Buy your own stationery), and progress towards BYODAC (Buy your own desk and chair). Hell, some of these beardie suckers you wrote about might even fall for RYOOS (Rent your own office space) if you can convince them that you're the hippest, newest thing in town.
To summarise article : money you save getting the fools who work for you to buy the kit they need for work will be offset by money it costs to handle all the different brands, OS versions, customisations, etc. Who would have thought that providing standard kit for everyone with standard configurations might work out cheaper?