In watching the show last season, I did notice that most all of the elements are off the shelf. Very few episodes have something truly Disney or truly imagineer created. The theme is Disney of course, but most of the stuff is store bought and slightly customized. (like the family's name on the engine) I still would love to have them come and do my backyard.
Is this one of the rennovation shows where they have a set time-limit for what they're supposed to accomplish? Also, I suspect that there is a certain element of trying to provoke people to buying things or at least swiping ideas (or appealing to viewers who would like to make things like that but never get around to it). I suspect it's an easier sell when its just a few customized off-the-shelf items instead of a full-on, designed by WDI backyard theme park.