Could you change your settings so we can be sure what Tablet you have, your profile says "none". 10 Hours is in power saving mode. Less in other modes. Simple, they advertise maximum life attainable, like other tablet makers. Depending on the apps you are using, items like live wallpapers, background processes and the like you will most likely get less. Be sure to read the Batttery Use link below.
Nits relates to brightness, TF300 max is 350. The TF700 max is 600. This makes it very bright for use outdoors for instance. How to convert brightness level to nits ? I don't know myself.