@Rushed Approach
It's ridiculous (to me being UK based) because the whole point about aircraft investigations is that witness testimony is protected from being passed on to law enforcement agencies in the UK - i.e. aviation safety is placed above criminal proceedings. Clearly it's different in France. The reason for this is simple - if you screw up and are going to be prosecuted for it, then you are going to cover it up if there is a danger you will be locked up, hence every pilot would stay silent in any investigation in case they might be accused of a "crime".
So yes the French system does indeed appear to be different, but not for the better as far as flight safety is concerned some would argue.
Ok, systems are different. Yours (UK) might also have problems IMHO :
take the case of a serious medical error, or suppose an innocent is put in jail, do you think that in order to improve the efficiency of these jobs in the future, one should also stay silent ? We all tend to ask truth about faults made by others, and aren't very prompt to tell it when the problem is on our side.