Let's assume, for the sake of argument, that Obama can convince all Democrats to support whatever dreck Grassley's dreaming of. Here's the list of the fifteen least conservative Republicans, according to DW-NOMINATE, that you would need in order to get to 75:
Olympia Snowe, Susan Collins, Lisa Murkowski, Richard Lugar, George Voinovich, Kit Bond, Thad Cochran, Lamar Alexander, Judd Gregg, Mel Martinez, Bob Corker, Orrin Hatch, Bob Bennett, Lowell Wicker, Richard Shelby.I don't know about you, but I have a hard time imagining what sort of health care bill can earn the support of those folks and not lose the votes of Russ Feingold, Sherrod Brown, Tom Harkin, and so on. Nor do I see how dropping a few votes from the left will pick up the votes of the next few Senators: Kay Bailey Hutchison, Mike Crapo, Mitch McConnell, &c.
The other way to think about Grassley's fantasy land is that health care for uninsured children, which is the political equivalent of a baby holding puppy wrapped inside an American flag, only got nine Republican votes. It's more or less impossible to believe that a more comprehensive restructuring of health care is going to get more votes than that.