Have the turnkey vendors actually succeeded in the pursuit of this dream? Most users of turnkey systems would say that they haven't. The reasons for their ultimate failure have a lot to do with their history, and their strategy of operation.
Their systems are very large (huge, gigantic, and other descriptors don't really do them justice). Large systems, even if the original design was modern, open, modular, and easy to enhance conceptually, ultimately turn into monsters which are intractable, closed, and which reflect no individual's point of view.
Secondly, the turnkey systems offer just a few solutions to customers' problems, and these solutions are a product of internal development. This not only guarantees that these solutions must be ``generic'' in the sense that they must attempt to solve everyone's problems, but that they will similarly fail to please all who use them.
Finally, the philosophical approach to the engineering design process reflects thinking which was current when the system was originally created which, in most cases, was a long time ago. The sheer size of these systems makes it a practical impossibility to make significant changes to them. This is why smaller, more focused companies such as PTC are having ``sudden'' success and are beginning to gain the attention of the users of traditional CAD/CAM/CAE.
Far from providing a totally integrated and automated solution to the process of design and manufacturing, turnkey systems virtually require that each step in the process is separate from the other. This is what the new technologies are intended to address.