I sometime work in the city and can often vary my hours as I like. If I am prepared to park a car by 9.30am and leave after 3.30pm I can get my parking for $12. If I park during the day it costs me about $5.50 an hour, up to about $21.
So, the carpark owners are managing the vagaries of having a product that is perishable - if the carpark sits empty on a day you'll never get that day back. So it seems they set an earlybird price so that they get at least some cash through for those spaces.
But the process encourages people to commute via car, to some degree. If I caught a bus at the same hours it'd probably cost me $8. The $4 gap is not really worth it, given the inconvenience.
It's probably time I start on my bike again anyway.