You are very wrong.
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All unibody MBPs will easily take a 12.5 mm drive.
However, almost all 12.5 mm drives are 5,200-5,400 rpm drives (maybe all), and thus somewhat slower than 7,200 rpm drives.
Check out this page
http://eshop.macsales.com/shop/hard-drives/2.5-Notebook/for
for a few good options. Especially the Segate Momentous XT and 750GB drive.
In contrasst to the psot above, I had a horrible experience with the WD Scorpio Blue, constant stuttering, stalling, beachballs etc etc.
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The Hitachi and Seagate 500 7,200 rpm drives work great in my 2009 MBP.