That is the theory, and that is what they tell you online, however since the other parks have seasonal closings, they allow the passes to be mailed out. And those are already "activated", rather than printing a voucher to later turn in at the window.
Most your perks are for your "home park", meaning the park the pass was originally bought for. But many people say they've still recieved the same perks at other locations. But usually monthly or during the summer, there's special coupons that can be printed or mailed out to you for your "home park".
I think part of the reason the pass is so much more expensive here is because there's 4 parks to go to in easy reach. If you're out in San Antonio, well there's only one park and closed during the winter months (so i've heard). The two theme parks are opened all year round here, and the water parks operate for about 10-11months out of the year.