It's a natural thing to do when you know the call is right. If you're unsure or think the call is wrong, you call for the chair to take a second look.
no, because that ist the job of you´re opponent, if its called in. Here we have a referee that most likely just had seen it wrong, went there, and overruled the linesperson, wich also don´t corrects the call/refree looking at the same mark. So it was clearly a wrong and bad decision, but i never would blame Nadal for it, simply because, many times on clay, way back from over the net, you cannot decide whether its in or out ... sometimes you can, and sometimes you cant.
Thats the point why in social matches (at least here in germany) if my opponent calls a ball out on his side i simply accept it, until it hits the fence before ... because its hard to see, and i have made a lot of wrong calls that were corrected, that i was certain i was right, and get it afterwards that i was completely wrong.
And, at least, in a Tournee, an Umpire gives me a point that he has checked and seen as correct, why should i question his decision. He has linespersons he also can talk to, he can see a lot better, he has replay and everything ... all this we also have on TV, but not the Players on the field.
And what I REALLY HATE is this thing that you just wanted to follow a mach, and to get whats going on without actually watching it, and all this Games with Participation of Federer/Nadal/Djokovic sooner or later explode because of this dumb mass of Fanbase morons (of every Player) sittig their arses flat in some betting office pounding their tapatalk and drinking the 10 can of Lager ... haven´t had played a single ball of Tennis, or even ever seen a tennis court in all their lives ...