Maui is a lot less crowded than Oahu, though it depends on where you stayed. If you stay near 'downtown' Lahaina, you will be charged for parking (or a few resorts in Kaanapali or Wailea as well). Similarly, in Waikiki you will almost always be charged for parking, and I guess they're adding that at Ko'olina too. There are many spots in Maui, and to a lesser extent Oahu that will not charge for parking. Mostly depends on a) the space premium and b) whether or not the resort thinks their guests will not be deterred by it (similarly to whether or not resorts charge for internet - if they think people will pay and not mind, they charge it, but if they think they will lose guests to other hotels with free wi-fi, they will not charge).
So charging for parking is normal - kind of. And much as I love Disney, they usually try to charge for everything. I'm one of the few who actually thinks the ticket price increases are okay, because it means that people who don't _really_ want to go, won't, which means its less crowded for us!