Robert Burns said:
You may then be doing the non offending team an injustice by making the scrums uncontested (definetly in Didds case). Have you actually ounished the offending team by making sure all scrums are now won by the side putting in and cannot be pushed?
There are 7 replacements, and at that stage of the game (WRWC Final) meant that there were still FR replacements on the bench. In Didd's case, it would be harsh (but technically possible).
With regards to the incident, from what I remember of watching it late at night and being tired, I thought the referee missed a trick earlier on by not awarding a PT or YC earlier when the scrum was pulled down again. England were dominant and NZ should at least have been warned earlier that further infringements would be dealt with more severely. With regards to the actual PT awarded, I thought it was a reasonably good call, although I feel in a way he made a rod for his own back by not dealing with it earlier. Out of all the penalties awarded at the scrum, the chances of a try being scored looked the least at that one, although on the basis of previous scrums, the total disengagement very early of the NZ back row causing it to splinter meant that the scrum beyond that point bared little resemblence to what one would expect.
With regards to the Yellow Card, it is true that a YC should come with a PT, the problem with the incident was identifying the offender (IMHO) as it appeared that NZ could have been penalised for a number of their players, and that the offence overall was probably not solely committed by one player.
On a side note, remember that in awarding a Penalty Try, the need in law for a YC is only there if it is an intentional offence (if I understand and remember the Law correctly).