Ok, well I will stand corrected about the exit-row not available for AS elites.
But I'm not giving in on exit rows to any other elite (NW included). I have been told every single time I book a ticket or I'm at the airport (except for the one time I mentioned above), that I cannot pre-assign exit rows (except for the current flight). Considering I live in SEA and have to fly AS a few times a year, I can't imagine 15+ agents have all told me the wrong info.
And, as a NW plat, the exit rows are NOT available for selection on the web when purchasing a ticket. The 12 exit row seats are always blocked. However, if you get to the airport early enough, they are happy to give you one. I highly doubt there are 12 people leaving the exit rows in place of "better" seats like row 28 :-D
-RM