This is why velocity is a 3 week average of points and can be overridden in the tool to show people who are out on vacation/sick. The tool dynamically updates to show what stories make it into an iteration as well.

The whole idea is not to force people into a box. It is to just give PM's a way to plan the future. Obviously, things can change so it isn't some forceful thing at all.

Don't knock it until you've tried it. I had an opinion like you and then I went and worked in this system and it totally changed my mind.