The purpose of showing is to "determine breeding stock". A spayed or neutered dog may be shown in AKC in brood bitch/ prodogy classes.
Showing is NOT a " beauty" contest. " If it walks like a duck, quacks like a duck"- ie if it moves right, feels right, looks like against the standard of the breed- judging each dog on against that breed standards- not the other dogs- and which ever one is the most right on to the standand is the final winner of Best In Show.
Some people think that training a show dog is a piece of cake.Just run the dog back and forth and done. A show dog must have a most sound temperment- able to deal with alot of dogs, strangers handlers in a tight quarters. Crashing crates, loud people, and excitment, and yet still go in the ring, have a total stranger put their hands all over the dog and continue to concentrate on the job at hand.

Yes i agree with you borzoimom, some obedience people don't realise how obedient show dogs have to be. It always amazes me how the dogs will sit on the benches, chained they may be, but they are quiet and calm whilst their owner is over the other side of the hall sometimes for an hour or more. I couldn't imagine mine doing that. I was surprised mine were quiet today in a cage while i was in the ring. With reference to this thread i thought it still was the kc rule that the dog could only be shown after spaying if it was due to medical problems, not from choice. Although i see that this is the case for you. Correct me if i am wrong , but it was only the other day that i was reading this. Was this out of date?

Yep, very out of date :smt001
The KC dont publicise that neuter status is no longer an issue and before their website revamp, the form for people to confirm neutering was tucked well out of sight [ unless you knew where to look ] but its easily accessible now [ finally ! ].
The form does not ask the reason for neuter to be declared.

Going back to the OP.
Answering the second part of the question, there is no yes or no. It depends on the breed and also the bitch in question. For instance in my breed, a spayed bitch can show a thickening of the coat and the coat turning curly. This is normally a good sign the bitch has been spayed. It isn't ultimate proof mind you and most bitches would not show any signs of being spayed, however it is an indication. If I showed my bitch in a line up of bitches, she would stick out with her coat, so I don't show her. Mind you I stopped showing her before she was spayed anyhow as agility was her thing so we stook to that.

I think people see it as permission as you MAY NOT compete at a KC show without the letter of confirmation from the KC.
I think because the rule is that you must have permission from the KC to medically change the confirmation of any dog.
Now neutering and spaying is a slightly different thing as the KC do not decide whether or not to give permission as they would with other operations. However when signing any entry form, any op comes under the rules and regs, whatever it is.
I think that's where the uncertainty comes. Acknowledgement from the KC of a spayed/neutered dog is in effect permission to enter at KC shows. It's just the KC will now, never refuse permission where as they used to. This still comes under the general terms though on any entry form.