I've noticed that if I have processed a RAW image (DNG) in an earlier version of ACR (6?) then attempt it in Camera Raw 7 I get the older options on sliders, specifically it reverts to 'fill-light' rather than the much better Highlight and Shadow options. This only happens in previously developed files.
There are significant differences between the new process (2012) and the previous process which means that convert an image from the old process to the new can result in significant changes that may require "correcting".
For this reason Adobe don't automatically change all your old images to the new process as you may well be perfectly happy with them as they are. Given that you can't undo the changes once made you might want to consider creating a virtual copy and updating that to the new process.
I love my girlfriend, my dog and my canon 5DIII - even though none of them ever do what I tell them
I am learning photo graphee - see the results at www.danmarchant.com