The Huhnes have not been convicted of swapping speeding points. They have been convicted of perverting the course of justice. This is a very serious offence, regardless of the relative triviality of the actions that, in their case, led to the crime. Those found guilty of PTCOJ are rightly sent to prison. There is no reason to think that their sentence will be any different from anybody elses who commits this crime, although an argument could be made that given the education they had and professions they were in, they were better placed than many other people to realise the seriousness nature of the crime they were committing.
Some years ago I was asked to fill in a legal form incorrectly which I would not do and one of the reasons I would not do it was because I knew that do so was a crime and if found out I would be prosecuted, end up with a criminal record and probably a prison sentence, and no, it was not DH or any member of my family who asked me to do this and I actually sympathetically understood why the request had been made.