Really? Wiki has him down as 1.87 m (6 ft 1 1⁄2 in), which looks about right.
That's weird, dunno where i got 6ft4 from then. Pretty sure i read that somewhere. I thought he didn't look that tall in the WC as well. Still though, 6ft 2ish aint half bad, and he's pretty strong on the ball.
Edit, http://www.transfermarkt.co.uk/marcos-rojo/profil/spieler/93176
1.89m here, just over 6ft2