Traffic wardens are a branch of the police and the tickets they issue are covered by slightly different regulations and they are also responsible for other traffic related issues. If you wish to challenge a parking ticket from a Traffic Warden it goes through the courts. Traffic Wardens do not clamp cars.
What you tend to see in most citys are Parking attendents who are responsible for issuing parking tickets only, they have no other role. Parking Attendants are employed by private companies on behalf of Local Councils and unless properly regulated and scrutinised can be a bit over zealous. You don't go to court to challenge their tickets you go to the local parking officer in the council. Parking attendants can authorise clamping and removal. IMO clamping is pointless as it doesn't remove the obstruction.
Scottish law prevents clamping ..... it is officially called Demanding Monies with Menaces after several people sucessfully challenged the law at it's inception in 1992.
As for the peeps that are saying he should have known he was illegally parked it's not always that clear. The parking regulations are extremely complex and unless you have some knowledge of them they are difficult to challenge, these private companies rely on the fact that people wont challenge because of the complexity. Everything from the road markings and signage, to the way the ticket is actually written is regulated and with a small amount of knowledge 20-30% of tickets can be successfully challenged.