Well since I produce science jargon for a living I'm pretty good at reading it, and I have a couple problems with this abstract (although in all fairness I'm totally not taking the time to read the whole article at the moment! ).

This is what I am taking away from this...
1) Yes, of course people who die with MS blame the MS for what is happening rather than other random things. We as humans like to connect bits of information together, so if we can draw even a remotely logical connection between what is going on and something we know about, like MS, then it will take the blame whether it deserves it or not.

2) People who are on drugs for longer periods of time tend to die more. This could be due to the fact that they are either a) older, b) have more pronounced symptoms, c) have had MS for longer periods of time and therefore are taking the drugs longer than people who have had it for shorter periods of time. This is one of those self-fulfilling prophecies IMO because you can see these same connections with statements like "People who have been drinking coffee for more years of their lives have higher rates of cancer!" when it could be due to a whole host of other things rather than just believing that coffee causes cancer.

3) Correlation does not equal causation. Ok, we know that people who were on interferons tended to have reduced mortality, but that doesn't mean that you can just willy nilly connect the dots and then assume that it 100% causes death. Science is sadly not that pretty.

All that being said, I do appreciate you posting, because I am an information collector myself I find it comforting to have as much information as possible so I can tell myself (correctly? who knows!) that I am making the best decision I can based on my knowledge.