Some, yes, but I see fewer and fewer 8' beds these days. Most contractors and corporate construction vehicles seem to be the higher trim variety with 5-6' beds and extended cabs.

You can still haul 4x8' sheets, you just have to be more creative and haul fewer at a time. Otherwise if you need so many you'd reach capacity in an 8' bed, you'd likely have them delivered to the jobsite (yes, even if you own a truck).