You make a lot of assumptions with your post. I am in charge of the infrastructure for a medium sized medical practice and we fully embrace the BYOD model. We have published guidelines about what is required on the computer (most recent service pack if it's Windows, most recent updates ubiquitously, antivirus software if it's Windows, etc.) and phones have a specific list of operating systems that are supported. Blackberry, Android, iOS in particular. We only support phones that have remote wipe capabilities and we routinely inspect our end user's phones for passwords.
While it is obvious that you want to take any safe guards you can to prevent a loss of critical data to unwanted hands (a HIPAA violation is what I'm talking about here), there's not really a good reason to not allow an end user's computer onto your network. You need to take the same precautions as deploying a new image into your environment. Not really that complicated.
I'm a little confused by the outright animosity at BYOD. End users are who we are here to support and, as long as we can maintain the proper level of security without significantly increasing the overhead, we should do all we can.