It's obvious that after 5 years of this program (or more) assigning civil 3d styles to the viewport scale was a mistake that was never caught when you (autodesk) bought the kernel. To this day, this has to be one of the most unneccessary backwards issues in the program.
If you make mtext, dtext, mleaders, blocks, etc. scale off the annotation scale why wouldn't you do the same thing for the C3D styles?
answer:
it was a mistake that never got caught
PLEASE FIX IT because it is illogical that my line/curve styles contained in an xref appear correctly in a viewport but not model space...
If your Civil 3D styles are contained within an xref, they will not change scale in model space, the only way to get them to change scale is open the source drawing, change the annotative scale, save the xref, reload the xref.
the comments at the bottom of this article sum it up also
http://www.civil4d.com/2010/07/civil-3d-annotation-scaling-revisited/
I want to agree with the original poster!! It would be great if Label Styles worked like MLEADER, MTEXT, and DIMS whereas, you can have multiple Annotative Scales assigned for each Label Styles. The beauty with Annotative Scaling is that, especially with MLEADER is that you can have different locations of the text for each assigned Annotative Scale.
I would like to also add the following request to Civil 3D Styles (Labels)
For 2....
This can be done through the label style defaults for the entire drawing.
That works for the "entire drawing" but only for one style at a time. If you have 100 styles in use....you have to change them one at a time.
Mark Green
Working on Civil 3D in Canada