The main source of the meme seems to be Brian Dunning's skepticblog bost.
However, a more thorough analysis posted later basically cautioned to abstain from as categorical a statement as Dunning's.
The analysis is "Steve Jobs, neuroendocrine tumors, and alternative medicine".
(NOTE: Upon further review, it appears to be a very close clone to Dr. David Gorsky's article OP linked, so it may have been an earlier rough draft of the same author, OR just extensive quoting by Dr. Gorsky since that article is bigger and appeared 3 days later).
I will provide his full closing paragraph (emphasis mine), but TL;DR is "We just don't know. it may have contributed BUT there is no proof at the moment".
If there's one thing we're learning increasingly about cancer, it's that biology is king and queen, and that our ability to fight biology is depressingly limited. In retrospect, we can now tell that Jobs clearly had a tumor that was unusually aggressive for an insulinoma. Such tumors are usually pretty indolent and progress only slowly. Indeed, I've seen patients and known a friend of a friend who survived many years with metastatic neuroendocrine tumors with reasonable quality of life. Jobs was unfortunate in that he appears to have had an unusually aggressive form of the disease that probably would have killed him no matter what.
That's not to say that we shouldn't take into account his delay in treatment and wonder if it contributed to his ultimate demise. It very well might have, the key word being "might."
We don't know that it did, which is one reason why we have to be very, very careful not to overstate the case and attribute his death as being definitely due to the delay in therapy due to his wanting to "go alternative." It's also important to remember that, as much of a brilliant visionary Jobs was, even brilliant visionaries can make bad decisions when it comes to health.
A pretty important logical step is shown earlier in the post. Though it's not a proof, it is pretty convincing:
That the surgeon opted to do a Whipple also tells us that there probably wasn't any evidence of metastatic spread of the tumor at the time. Otherwise, I doubt the surgeon would have recommended as huge of an operation as a Whipple just for palliation. Indeed, Whipple operations are generally done with curative intent and only very rarely done for palliation.
The morbidity is too high to justify doing such an operation when it can't save the patient's life. In fact, it's not unreasonable to infer from the willingness of the surgeon to do a Whipple operation that, as far as could be determined, Jobs' tumor was still restricted to the head of the pancreas and thus still potentially curable, even after nine months' delay.
Meaning, that it's likely that the cancer did NOT indeed spread as much as had been asserted during the 9-month "alternative treatment" delays.