WT? Black Bars Onscreen with BD?

[shug7272]

I thought movies on Blu Ray were to take up the entire screen and not have the letterbox bars of the old DVD fasion. I picked up MI3 per the advice of several members here (kicks ass by the way) and noticed the letterbox bars. I thought this was a thing of the past with Blu Ray. Why do I need a widescreen high def 1080p television to play a 1080p signal only to STILL lose some of the screen to black bars? I hope it is something Im doing wrong cause Im pissed.