Why does this not work in Camera Raw 6.1?
Because Camera Raw is a plug-in and limited by the API of the plug-in environment and Lightroom is an application that can do things that plug-ins can;t. Note ACR can do some things LR can't. So, the bottom line is that while the Camera Raw/Lightroom processing pipeline is capable of rendering images exactly the same, the usability and the functionality is going to be a bit different.
thank you very much for your reply. It was certainly helpful and explains my experiences with the two.