Firstly if he expected it it wouldnt be unexpected.
Secondly, If Zambrotta had done what he would have 9 out of 10 times, then Messi would have been free high up the pitch and Scholes would have been out of position giving Barca a good attacking opportunity.
I can see your point, but Messi was playing the odds. If it had come off as it would have 9 out of 10 times then youd probably be saying the opposite, that Scholes should have been tracking Messi. You cant play based on the 1/10 chance. You have to play the percentages.
Messi will score more goals each season from being free up front after not tracking the run when his own team has teh ball, than Barca will concede from Zambrotta making the unusual mistake