@James1485 The overall rating is not an aggregate of the other star ratings. It's a completely separate rating and the only one that is used for the Superhost status (although if you got consistently low star ratings for cleanliness, for example, you'd get warning messages from Airbnb to pull up your socks). Star ratings are talked about on the forum here a lot, and most hosts are displeased in some way with the system. For instance, a guest may rate you 5*s in all the separate categories and then 4*s overall. It's bamboozling.
As to why it shows in basic stats differently than it shows on the Superhost stats, I've noticed that the ratings don't always match up either and don't know why. The first may be based on your ratings since you started hosting (not sure about that), the Superhost is definitely only for the past 365 days.
And no, they don't round up from a 4.7 to a 4.8. They'd round up from a 4.65 to a 4.7, though