"I have never found myself needed to have a pair of scissors for something a knife couldn't do..."

I think this is another case of differing "style", approach, whatever, as in backpacking I've never found a use for pliers but I use the tiny scissors on my 0.8 oz pocket knife a lot more than I use the blade. The scissors allow for much more control when trimming a blister, cutting duct tape or whatever to protect the blister, trimming finger- or toenails, making gear repairs, cutting holes in a yard waste bag to make a hasty rain tunic, ... cutting anything where a higher degree of control is desired.

What I can't think of are [m]any examples of things that I'm likely to encounter where very small scissors couldn't do what a knife blade can.

I'm not saying that the pliers aren't a better choice for some people, folks who do different things in the woods or approach problems differently than I do or whatever ... just that for my personal backpacking style, very light & small scissors are the no-brainer choice.