The difference being that I don't want someone to think that because I rated something 2 out of 5 that I didn't like it because it's less than 2.5. And for most people, a 3/5 doesn't mean "yes, I heartily recommend". But they can believe it for 8/10

(Actually, 7 points as someone else pointed out - by my point stands even with a 7 point system).