I'm not sure but there are a few weirdnesses with assigning components content to variables in scripts.
I've been burn by terribly counter-intuitive behavior, but I don't think it applies there.
Maybe someone else will have an answer for you...
here:
Edit:
Actually it does apply there.
If something changed the value in your input component...
You'd expect the input to be a constant, but it's actually not.
But there's no reason it would work with the in version...