Very interesting blog Ross. Most is accurate but honestly the PA is based on least common criteria. I see you don't suggest Virtualization but Exchange and Windows still have the same issues that makes Virtualization effective which is changing workloads, underutilization of systems, and overall system maintenance. With the limited amount of overhead the a hypervisor provides it seems that it would actually provide more scalability than physical hardware if configured properly. It also eliminates the inherent issues with cluster networking problems that have plagued not only Exchange 2013 but also Exchange 2010 which is more OS related than Exchange.
Also, have we seen performance benchmarks for Bitlocker and Exchange 2013 yet? I can't seem to find them.