That's not really accurate though, and I will give an example as to why:
Did you know Elizabeth Warren was once a Republican? Even after she became an academic, she believed for instance that people who got foreclosed on were in general delinquent, and it was not the banks fault. Then she set out to prove this. It was by performing an extensive study, interviewing and meeting with foreclosed homeowners in the 1990's that she came to the realization that many of those who were foreclosed on because of lax regulation and predatory lenders.
I am just trying to show that your generalization is inaccurate. There are many other examples (for instance Joe Sestak) that I could name, so it is not only Elizabeth Warren.
I think the assertions that Amy Klobuchar would be a better general election nominee than Warren is just crazy. For this and for many other reasons. I think the average voter loves politicians with passion for the middle class like the one Warren has got.