Hi Malyla -
It was a way to encourage the large percentage of folks who do lurk to register, contribute, and take advantage of many of the features blocked to folks not logged in. It also discourages "spiders" who crawl the net for posted email addresses, etc.
I get the office thing. It may not help but did you know that there is an "invisible mode" so you can be logged in but not be seen? http://www.tsptalk.com/mb/profile.php?do=editoptions
I am interested in your feedback and I will take the block away for now, but will show the "why not register" message.
For those who don't see it, the "block" had kicked in after 6 page views from non-registered / not logged-in, while the "why not register" message would show after 5 page views.