Machine Design is a bespoke engineering practice. That means you come to them with a problem and they work out how to fix it.
The site was designed to showcase projects that they have been involved with as it clearly is not possible to specify the problems that they will solve for their client until the client has identified the problem.
DNN seemed a good choice at the time, however quite honestly the things being done by this site could be achieved in either DNN or WordPress. I would probably skip the flash today as a matter of course as apple have decided to not allow flash on their devices.