3) John Kerry lost an election because of accusations of hypocrisy that were arguably not true. What makes you think that accusing a Massachusetts politician of hypocrisy that manifestly is in fact a thing would go any better for the target?
Mitt Romney hasn't flipped on national health care at all (he implemented a state plan) 1) Which is a distinction most Americans won't notice.
2) Mitt Romney also appears to be pretty incoherent/out-of-touch.
1) The issue is noticeable. Romney has campaigned on the issue of repeal for 2 years now. Nobody cares about what happened in Massachusetts 10 years ago. All bringing it up does, is make him look centrist and reasonable.
2) I don't know what you mean by "appears" exactly, but he obviously isn't incoherent and he is less "out-of-touch" than Obama is or Kerry was/is.
3) I think it is interesting how leftist-ish democrats always come up with simple/wrongheaded excuses (usually involving some supposed republican dirty trick) as to why they lost an election. Kerry didn't lose because of "flip-flopping" and Dukakis didn't lose because of "Willie Horton." They can never accept that they were wrong on dozens of important policy positions and america correctly rejected them on their merit, so they invent folklore.
I would argue that presidential candidates lose when they run as hard ideologues (e.g. Gore and Kerry as hard liberals and Goldwater as a hard conservative) and win when they campaign as centrists.