Park skating is skating within a controlled environment, during designated hours, usually for a designated fee. And then, you have to follow rules, and wear pads. However, provided you can comply with all the 'rules', you are guaranteed a hassle-free time. Sounds like a catch-22 to me. Another difference is in what you want to skate.
Some people are rather park-specific, and some people are strictly street skaters.
So, transitions are strictly park obstacles. You can ask any street skater and they will tell you, at great length, that angle iron and concrete are not the same. Granted, some parks do have concrete ledges, but after a month they are all chunky and terrible. I have yet to see a park that maintains their ledges. The same goes for handrails.