Murtha and Rangel are in more hot water from a legal perspective but Nancy's political drama is far more compelling and has already garnered infinitely more attention from the press. It's a credibility/leadership issue rather than a legal one. Plus if Murtha or Rangel were ever Speaker while their scandals were unfolding they'd likely be gone already.
I'm sorry, but I witnessed far too many compelling political dramas where Republicans made asses of themselves in the last eight years and easily survived to think that this one, which Pelosi is fighting back on, is somehow going to kill her career. What exactly has she done that's going to lead to her ouster? She's fighting back, and she's got some strong allies in Bob Graham and Obama. Newt Gingrich and Steve King calling for her ouster is not going to carry any weight in the Democratic caucus.
This is like thinking that "arsenic in the water" was the silver bullet that was going to take down the Bush Administration in 2002.