Scott: Whilst you're correct in what you say, I believe that in that case we were talking about being told to be level by a certain point and then being cleared to one beyond. The consensus then was that the original level restriction was cancelled (not something with which I personally agree as sensible).
In the case here, I would argue that as you are still going to the same point, you should still comply with any restriction based upon that point unless specifically advised otherwise by the controller. In the case given here the clearance really is: "Descend FL120, cross GWC 130 or below".
I have long believed that this issue should be resolved by the insertion of something along the lines of the following in the AIP:
"A clearance to a new point along an aircraft's route does not remove any restrictions given with reference to intermediate point(s) unless specifically stated by ATC."
OR:
"A new clearance in a horizontal sense does not negate a clearance or restriction in a vertical sense unless specifically stated by ATC."
There is far too much doubt in some pilots' minds about this. Just remember, in the UK many of these restrictions are given to keep you separated from traffic on crossing routes or to keep you outside the airspace of someone who is not expecting you.
Like all of these things, however, if you are not sure at the time, don't ASSUME, ASK!!