I'd have to disagree with that there. Looking at the Spanish players, I'd have to say that the majority of them are a level above what we have in the Premier League. Xavi, Iniesta, Fabregas and Alonso are all above what we have here in my opinion. I'm not counting Busquets because he's more of a defensive midfielder.
Alonso was a very underrated player at Liverpool in my opinion. The fact they wanted Barry to play ahead of him really shows how much they underrated him to be honest. His true impact there was only felt when he left the club. While people spent most of the 2007-2009 period praising Gerrard and Torres to the heavens, they almost completely forgot about the man who provided Gerrard to provide for Torres, the man who dictated the play for them. That was Alonso.
Anyway, to answer your question, I think there's one noticeable difference between their players and a player like Carrick. There are games when it won't look like their is too much of a difference, but we see it when teams play a high pressure game against us. Carrick is suddenly nullified in the middle and can't play his usual game, because of the lack of time he gets on the ball.
What's the difference with the Spaniards? They thrive under high pressure. Instead of losing the ball a lot and struggling, they use it to full effect by exploiting the spaces at the back that are left by high pressure opposition. That's why teams don't dare play a high pressure game against Barca, while those who do often find themselves being ripped apart.