B737 Manoeuver speed

[TyRod]

Hello,

I was reading the fCTM the other day and noticed something about the minimum maneuver speed.

It says that below 20000ft or with flaps down, the amber band gives you 1.3g before stick shaker.
Above 20000, it gives you 1.3g before low speed buffet.

Can someone explain me why such difference have been made?

Thanks