either A: you are secure in your product and therefore you have nothing to hide and WANT it reviewed so more people will know how awesome it is before it hits the shelves...
or B: you know you made a subpar game annd want to still make a buck.
Point is there are embargos on VERY good games' reviews (Mass Effect 2, Arkham Asylum etc) until AFTER the day of release and there are gaqmes that are very mediocre (yar's revenge coming out the 29th) that are ALREADY reviewed by the specialized paper press
so.....again.....what's the point???