Photoshop 6 (not CS6) had major colour handling changes, that were a greatly needed correction from the mistake that was made in 5.x. Over the years there have been minor updates that have helped graphic arts users, however they have been few and far between.
I agree that the focus of Photoshop has drifted away from graphic arts and into the web and photography, this is only natural as Adobe are not going to make any serious revenue from the print graphic communications sector.
As for the OP, I have not yet looked at CS6 (still on CS5). What Adobe plug-ins are missing? Over the years Adobe have dropped or revised plugs or other features, nothing new here. Where possible Adobe generally try not remove features... Or are you referring to support for 3rd party plugs?
I still keep CS around so that I have access to ImageReady so that I can make the rare animated GIF without having to have a license for Photoshop Extended!
Stephen Marsh