Quite a drawback for majors, as this decision will hinder all the law actions they're currently handling : as they'd never accept that, they decided they'll try and have the sentence broken (this is "cassation").
If you don't know how justice functions in France, just lean that cassation court won't have to decide about the affair itself (ie piracy), but on law, formal issues. If there's been a flaw in procedure, the judgement will be broken and a new trial would ensue.
[Upd.] Here's Mr Freeze quite professional comment:
The cassation court judges only about "law issues" of the decision, as opposed to judges in 1st instance and appeal who judge "in fact and following the law". 1st instance and appeal judges must establish what's "really" happened (X downloaded such song, burnt such soft...), then apply the law accordingly to the the facts (x is found guilty of illegal reproduction of copyrighted music). Cassation doesn't have to go back to the facts that were established: they study the law consequences attached to the facts the judges established. That's what you'll call the facts "qualification". Of course, in the appeal trial, a formal rule might have been violated, which cassation will condemn if there's an action in that direction; yet this is not the most common case: it's even the most insignificant as far as law is concerned!!
To conclude, in the case you've described, cassation could sanction the appeal court for for inducing wrong law consequences of the facts it has established, which is much more fundamental than a plain "formal vice": right itself would be then changed, and it's cassation arrest that will be reputed jurisprudence, instead of that of the appeal court... It is almost the most important moment of the procedure, and not some extra, optional moment of it.
So going to cassation could result in a change of the whole affair !!! If they say the facts required a condemnation because of a law violation, the appeal court where the ensuing trial would be held would have to judge the facts accordingly!
