I believe teams with greater reputation usually get more 50/50 calls to their favour throughout the season, but the reactions get amplified when it comes to Barcelona and Real Madrid. But, during these last few weeks, Sevilla robbed Betis for the second time this season (offside on N'Zonzi on the winning goal), and there are probably plenty more examples during each gameweek that we don't necessarily hear about.
However, the same teams sometimes have to pay for their great reputation, because sometimes the referee wants to prove a point in toughness by having a secret personal agenda against either of these teams. I think Barcelonas last 3 weeks is a perfect example of that. When they were vs Betis, the ref and the linesman ignored Neymar being flipped over in the penalty area, and in the very same sequence, barcelona had a ball clearly inside the net; but the refs chose to believe that it was cleared off the line. 1-2 weeks after that game, Neymar seeks a penalty by jumping into a Leganes player, and the ref folds and awards barca for penalty. Give and take.
What bonds us La Liga fans together is that spanish referees frustrates us all; I honestly believe they are the worst ones in Europe. It is not necessarily because they make the wrong calls, it is because they keep an extreme inconsistent level throughout a game. During a typical La Liga match the referee can decide to play mr.sensitive and book anyone for virtually anything, and the minute after he would ignore someone who is being assaulted. As if they only have one rule when being a referee; "Improvise!".
I understand that being a ref must be the worst job in the industry, and it takes a lot of character to put yourself through it. But I honestly believe that some of these spanish refs don't seem to have good intentions when they're refereeing during a game, sometimes it is more about their pride and ego; that is why some of them deserve the heat that they get. I really dislike the job Mateu Lahoz is doing, and can't wait until he retires. To this day I am so happy to never see Mejuto Gonzalez, Medina Cantalejo or 'Gargamel' (Iturraldo Gonzalez) in a La Liga game ever again; and I believe every single on of them deserved heat and critisism.