All i can think it would be is simply either a company requirement in their AOC or insurance requirements of that company. If you have a CPL, and your CSU and R/G stickers in your logbook, as a technicality, your free to fly any single engine piston a/c below 5700kg, but it makes perfect sense to do some time in the 182, before you blast off doing charters or meatbombing for a company