The economic solutions to Medicare are complicated. Neither side has something easy to understand for the average person without serious study and probably education in economics and public policy. I doubt that the question of whether Obama’s plan or Ryan’s plan would take more from the system is very relevant to them. What is maybe relevant is that Obama's reductions would not be very directly visible to the end user.
People recall George Bush's desire to privatize social security just prior to the collapse of the stock market. Some people also don't listen well and don't spend a lot of time trying to understand things they are confused by, but they may very well recall an impression they had that someone wanted to reduce their security, while perhaps orchestrating an enormous, unprecedented “giveaway” of their money from government to the wall street private sector. Ryan’s plan may, rightly or wrongly, bring back such thoughts.
Some people can be greedy. I heard an interview recently with some Medicare people reveling in the fact that they got hundreds of thousands of dollars health care though Medicare but didn't have to pay anything for it. They didn't see this as generous or lucky, but rather as well -deserved and not to be disturbed for themselves or their children. They don't want to pay more for it. Some said they were Democrats, but some also said they were Republicans.
The elderly, people on Medicare, constitute an enormous, motivated voting block with a lot of time of their hands.
So, I think lots of people on Medicare who get out to vote will not vote for Romney/Ryan because they think Republicans want to do away with their current security, even if they could save the system for someone else after they are dead. It won't take much of a shift for this kind of thinking to influence the election results. People may be disgusted with Obama, be tired of him and disappointed, but they have little real reason to trust the other side with their security. The Democrats are bent on giving away government (my) money like drunken sailors, but many elderly suspect the Republicans will too, just to different people.
The Good Doctor