Our company supports limited BYOD which are only allowed to access our network via our public wireless network. I think I would prefer to purchase the device of my choice as well because the devices provided to us by the company are rather low quality and low power. Fortnately I am able to purchase my own keyboard and mouse which is probably what I am most picky about.
It seems reasonable that a company could easily support a BYOD model so long as they laid out a set of standards that a device would need to meet such as Anti-virus, etc and made all devices connect through a firewall with some of the more advanced security features.