Smalma...good question. I think it gets down to the "close to home" syndrone.

When a salmon is caught in the salt or at the mouth or the Columbia, the fisher has no idea where the fish is headed, so "it's probably going to a healthy stock watershed" is the logic. Now, when we catch a non-clipped salmon in a actual spawning river we "know" that this is where the salmon is from, so therefore we "coudn't possibly kill this wild salmon" because "X" River needs all the wild fish it can have.

Therefore, when we catch a salmon when it's "close to home" like the way most steelhead are landed it makes the issue way more black and white. Rather than like catching a un-clipped king at Astoria or Neah Bay, we don't know where that fish is heading and we're pretty sure it's not going to be going to a depleted watershed ("what's the chance of that" is our logic) so it's not "close to home" therefore we justify to ourselves that bonking the "big beauty" is just fine!

So in closing this long winded description, it gets down to most steelhead are caught in their native river, so we know how healthy/unhealthy that river is, where as a large % of the salmon are caught during their migration so we don't know where that fish is going and it's human nature to deny that we're doing any harm to the wild salmon becasue we justify to ourselves that it's probably going to "Hanford" etc (supposed healthy run). It's like some people want Alaskan Giant salmon released but they have no problem supporting the bonking of Washington/Oregon giant (proportional) kings that are probably "native" fish. Just food for thought.