True of most cars and trucks I've driven. I think it's because the front is designed to do most of the stopping, that's where the weight is shifted when stopping. So, the front brakes are set to do most of the work, the back brakes are just for help. I bet if you hit the brakes hard while going in reverse the front brakes will lock up long before the rears do.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k