Why in this age of miracle technology is it still so hard to just show someone something on your screen?

If I'm looking at a diagram, and my co-worker is sitting two desks down from me, it's still easier for me to turn my monitor or have him walk over than to just send the image to his screen.

The right solution would have to need zero configuration, maybe the receiver broadcasts “okay, I'll see” and then your machine finds others advertising they are ready to be shown the screen and you attach to them. Obviously networks of machine that trust each other is necessary, but that can be solved.

There are oodles of companies hooked on showing a whole screen across thousands of miles for web conferencing. But I just want a way to show my wife a cute photo of our son on her screen from the other side of the room. And I don't want to have to permanently be on IM. And I don't want to write scripts to hack her machine. I just want to right-click, select “show to wife” and have her accept the request. Is that too much to ask?