No corruption—what Richo said is absolutely spot on. When you're a bottom team, you rarely get the rub of the green, and subconscious bias often creeps into the refs' decision-making.
There’s a way to analyze whether this is true: hire a company to review every penalty and create a rating system to classify them as obvious mistake, likely mistake, 50/50, correct call, etc., and publish the numbers for each team. You’d also need to include six-again calls and bunker errors. While some may argue there's an element of judgment involved, there should be enough data to reveal any trends. Provide the company with the NRL rule book and instruct them to follow it word for word.