I haven't done code reviews in forever, but when I did them, sure there were some things that were plain wrong, but there were also a lot of things where I wasn't sure if it actually needed a change - a confirmation from the developer would be required.

And then there's things that I would like to see changed, but as a personal preference; when it comes down to it, it doesn't make a difference and I don't really care, so I would posit it as a suggestion instead of a command. Mind you, if I didn't really care either way, I could've chosen to ignore it as well. But you know how some people get <_<