I think you are a bit unfair to Grado now. A Gold doesn't sound as a Black or Blue even if the cantilever and stylus is the same. First we have the thing with sample variation, all cartridges has this. This means that no stylus, cantilever or generator is 100 percent identical. So what Grado do, is that they sell those cartridges and stylus/cantilevers that meets a tighter or strict tolerances at a higher price, because they perform better in their own in-house tests.
I like this idea, because you know what you got. The maker has done the selection from the production and clearly labeled them. Then it is up to you if you want to pay for the better sample or not.
Then they have changes in the generators etc, exactly what those changes are - well I have no problem with them being tightly lipped here.
The specifications differ:
Frequency: 10 Hz - 55 kHz (Blue and Red), 10 Hz - 60 kHz (Silver and Gold).
Channel separation: 30 dB (Blue and Red), 35 dB (Silver and Gold).
So something has been done.
As for their headphones, they don't sound the same. I have the Grado SR60 and love mine. I have auditioned the SR80's and do found them to be better, but not enough for me to swap my 60's for them.