In reverse, T and Z players in the EU servers are less aggressive on the average compared to Koreans who specifically add in harassment whenever they possibly can (trading as effectively as possible at different points in the game). Both T and Z simply want 3 bases and reach toward max with upgrades rolling fast. Obviously players want to deny their opponent's 3rd, but they'll put much less strain and effort on their opponent on average.
Thus when transitioning to Korea and korean opponents in international tournaments, Protoss is already fighting the "metagame" style of the other races that force a protoss to slow down. In comparison, a TvT MU between a korean and foreigner could be a strange reaper into mech opening for the korean with a hellion drop/runby behind reapers and the foreigner might just forgo extra defense and counter aggrssion to grab a greedier 3rd or tech up/upgrade faster. One mis-step by foreigner and he loses the game in some cases, other times one bad decision and his macro advantage is gone, etc...