So if you're travelling from the other end of the country, as is the case whenever I visit, pay the extra £80 or so per night to stay at hotels on the transport network, pay a small fortune to travel down from the north-east, deal with tubes, deal with trains etc... yeah, that's a great option compared with driving and travelodges. So sod public transport. If you're travelling long distances, it's only a realistic option if you have no other options.
So, you pay for parking. That's an extra £5 added to the cost of your day, for what? If they jacked ticket prices up by £5 instead, people would be screaming blue murder. But when they charge you for sticking a car on a field full of gravel and charge you instead? No, that's just fine with the world.
It's not the end of the world, but I tend to call things as I see them, and this move is motivated entirely by greed, pure and simple. Merlin know their visitors have little choice but to bear the cost, so they're jacking their prices up to the maximum the market will bear.