i will fly YYZ-SFO on an A320. at booking time i reserved seat 12A (first row of economy). however according to seatguru it has slightly reduced seat width. is that true? if so, why is it a preferred seat?

http://www.seatguru.com/airlines/Air...bus_A320_B.php

(on seatexpert it moreover says "Unconfirmed reports indicate that rows 12-16 and 29-33 have slightly less pitch at 31 inches, and rows 19-28 are a little roomier at 32 inches.")