@ Brian - While I agree with your comment in essence - "What IT professional installs a major patch into a production Exchange environment without testing properly themselves in a lab environment?" - I present you with the following question - What IT professional realistically has the resources of the Microsoft Exchange quality assurance division? My point is that if Microsoft Exchange team and their 100,000 automated tests do not uncover an issue, what chance does any "IT Professional" have. I accept in this instance it can be uncovered by typical usage of Outlook, but as a general rule you'd expect to have less resources that the company that develops the software you pay for, otherwise you'd be writing it yourself?
+1 for appreciating the open explanation.
My 2c.