standard brakes in Mx-3

[valdigre]

I have this question about standard (crappy) Mx-3 brakes. I know that most of the braking power is on the front side, but I was wondering if it is normal for the rear pads to use about 60 % of the rotors' surface. What i mean is that front rotors are all polished, but the rear ones are polished in about 60% (center part) meaning that either this is normal or my breaking pads suck...
What is your opinion about this?

[valdigre]

and btw, what braking pads do you recommend? Is it worth buying some better pads without rotors, because I can't afford it all and some better braking power would be nice...