I've found this to be true pretty much across the board. My mechanic tells me that if I don't give a 5 score (on a scale of 1 to 5), they get dinged. Most surveys that I've seen report the percentage of scores in the 8-10 range (on a 10 point scale), sometimes going down to 7, as the good/acceptable scores.

A company I worked for had ratings of not meeting expectations, meeting some expectations, meeting expectations, exceeding some expectations, and exceeding expectations. Meeting expectations was considered to be a poor rating - the bottom two were reserved for folks on the way out. So meeting the expectations for you job was considered somewhat unacceptable.

I pretty much give 8-9 when there are no problems, 10 in an area that a property excelled, and below 7 when I'm not satisfied.