This is a complex issue with more to it than simply daVinci vs. open prostatectomy.
As Tony writes, experience is a key element, but does quantity always equate to quality?
There is the patient's own physiology to consider as well, for example, how difficult is it to tease the nerves away from the prostate? (Not all prostates are alike)
What about the extent of the cancer, capsular penetration, extracapsular, lymph node involvement, etc?
What about a man's state of health going into the surgery? Diabetes, heart disease, ED, and other illnesses may impact recovery.
There are many other questions that could be asked that are important considerations in evaluating prostate cancer treatment "success".
Any straw poll here would be nothing more than anecdotal evidence that is meaningless. To be scientific a study must be well designed and involve thousands of subjects, which the study that started this thread discussion was not.
As a side note, the hospital where I had an open prostatectomy has since purchased a daVinci robot, which it is advertising to prospective patients. Now they are pushing surgeons to use it so they can justify the enormous expense. Go figure!