Any hotel you stay at (and use a credit card at check-in) puts some sort of hold on your credit card. Typically, this amount varies from between $100 per night to up to $500 per night - depending on your room rate and whether incidentals can be charged to your room. Sorry folks, but this is a general rule practiced throughout the US hotel industry - and it's their way of insuring they get their money when you check out. You are probably just surprised at this because the HRH has the honesty to let you know this up front. The $300 per night sounds reasonable, it's right up there with the hold that the Disney hotels put on their guests' credit cards.
Of course, you CAN ALWAYS stop the hotel you are staying at from doing this check-in. Don't forget that, at a minimum, a hotel needs to insure it has guaranteed payment of room and tax for the number of nights of your reservation. Also, you will not be able to charge anything to your room - this is typically printed directly on your room key.
But don't worry, if you choose this option you will still have Express access to the attractions.