Now don't get me wrong- there are some GREAT concrete contractors out there but the process necessary to create a proper concrete skatepark is simply not something that most contractors are willing, or able, to provide. A skatepark is more like a HUGE concrete counter top, perfect in every way, hand rubbed and polished to perfection... only we have to do it with curves, angles, vertical faces, steel edging and, most importantly, we have to do it without cracks or expansion joints.
This crack occurred in a skatepark before the it was even opened. Obviously poor attention was paid to the substrate (dirt) compaction or rebar placement within the slab and the customer is left with a safety concern before the park even opens!!

Skatepark builders not only have unique skills but unique tools and very unique motivation... we skate and understand that a broom finish hurts, a radius needs to be perfectly tangent at the bottom and coping needs to stick out JUST the right amount...
The best analogy is to ask if you've ever tried to tape drywall... without the ability to sand it when you're done!