If one of them said they liked it, it would be approved, wouldn't it?
That's what I think too. Also being a mod and going through thousands of images probably skews your sense of quality since you might feel that you aren't doing your job if you approve most of the images you see, but then again, danbooru users are pretty mature in only uploading relevant and quality images.
The only way that a number is recorded up at the top of pending images is if an approver clicks the link associated with it; the links appear on the modqueue page and at the top of each image page that the approver hasn't clicked one of the links on yet.
As seems to always be the case in this world, we solved one problem and it created another. Instead of people just assuming that nobody ever saw any of the unapproved images, people get insulted as the number of people that don't want to approve them climbs.