A couple of people have mentioned that airlines besides Southwest (AA in particular) don't have this policy. I keep seeing the following text in AA routings, though:

RULE 6020 DFR3 PASSENGER OCCUPYING TWO SEATS APPLIES

Of course, the closest thing I can find through Google about "rule 6020" is some sort of youth soccer regulation.

As a person of size myself, I try to be sensitive to other passengers that might be seated next to me -- I always book aisles, take seats in the back of the plane (even on a Super 80 )so I can get an open seat next to me, and ask to move if I'm seated next to another PX and can avoid it somehow. And I'm trying to make elite now so I can start getting upgraded to seats that fit me.

There's only so much maneuvering possible, though, and here I think the airlines are partially to blame. While I am admittedly overweight -- although I can still sit in fixed-armrest exit seats -- I'm also 6'2" with a big frame. No matter how much weight I were to lose, my shoulders would still be several inches wider than a coach seat -- and that's what ends up being the biggest problem for me. If I'm seated on a full flight, I end up spending most of the time leaning sideways and getting jabbed by the drink cart so I can avoid elbowing the person next to me.

Americans are, on average, several inches taller than they were when a lot of these planes were designed, and yet seats keep getting narrower. I'm not sure what can really be done about it, but it seems like there ought to be a solution of some sort. If any airlines implemented something like MRTC or E+ with extra space between the seats, I'd switch my allegiance overnight.

d.