Hah! I literally JUST wrote a post about how I sometimes round off my score half a point up or down from where I think it actually is, according to where its overall score is compared to where I think it should be, so this for me was a 7.5, but I scored it an 8, precisely to "balance things out" - obviously, I'm not that much of a fool to think that my one point would make a difference - it's always going to be a drop in the ocean - but it's my way of rebelling against the inflexible imdb scoring system - they should definitely offer half-points at least! (Yeah, I know, I'm James Dean in Rebel Without a Cause. ;))
Besides all that, my scoring can actually sometimes fluctuate even from day to day, depending on some possibly not altogether objective factors, like mood - in fact, your nicely put, concise reasoning has convinced me it really does deserve the full 8! So fickle! :) - and over the years, obviously experience has forced me to reconsider and adjust some of my past scores too. I wonder how many people go back and revise their older scores. If they were honest and cared, everybody would.
"It's too late... Always has been, always will be...