The Habsburg situation is rather unique. The lay of the events that transpired took away any justification for Austria to have Magyar and Slovak, they didn't even get the CBS.
Historically however , Italian culture is very justified for Austria, it is just ussually left out for game balance reasons, in that Austria ussually grabs most of Germany and Hungary anyways. In this case, Peter has shown exceptional adherence to the spirit of the rules and has done no such thing.
Eventually, after he loses the Netherlands, he will become very ahistorically weak, which would not make for a very interesting longterm game. So, a single special allowance was made for this single special circumstance that he should get Italian culture upon choosing to keep his italian provinces and let the rest go to Spain.
Ottoman Empire, France and Austria agree to this. I don't see why Portugal cares, since we've given the most thought to it. Can you give any real argument Smirfy beyond a single line?