Chris -
I'm probably the last person that should be answering this, given that I've played few holes that were "copied" from other holes. Nevertheless, I'll give it a stab...
There are really only a finite number of permutations of holes, given all the contraints - e.g. straight, dogleg right, left, etc. If you read enough threads on this board, you'll see that virtually every hole discussed has analogous holes from courses built many years before, regardless of whether or not the architect knew of the predating hole. This also explains partly why one doesn't come across many, if any, "new" concept holes built recently. Just look at the person above who classified the modern island green as simply another Short Hole, albeit a more penal one.
Additionally, when architects build these "copies," they are generally not copying the hole so much as the concept of the hole - ie. how bunkers, angles, etc. influence play. What makes the copies interesting is that they frequently have variations, especially if the architect has been careful to preserve the minute differences that nature gives them. The poor copies tend to force holes on terrain that isn't well suited, or simply bulldoze over natural features that could have given the hole something unique when compared & contrasted with the original.
If you read some of the threads of the famous named holes, I'm sure you'll see that the differences, even if they are minute, give rise to some pretty interesting(& sometimes even heated) discussions.