from what i can recall, it was to end the question over whether probate was just a state, or a federal, level, issue. (which i believe is ultimately tied to a fatter take for the IRS)
http://www.law.syr.edu/Pdfs/0May222006_Lawyers_USA_Anna_Nicole.pdf
While the Court made clear that basic will contests will generally remain the purview of state courts, jurisdiction experts say the case opens the door to fresh attempts to steer some probate litigation into federal court.
“The ruling reduces the presumption of finality and exclusive jurisdiction of the state probate courts, creating an opportunity for far greater litigation” in the sometimes contentious world of probate, said Jonathan Turley, a professor at George Washington University in Washington, D.C. who comments frequently about the Supreme Court. “The Court has affirmed that you can create a second front in a probate case by declaring bankruptcy.”
http://www.cnn.com/2006/LAW/05/01/scotus.smith/index.html
State courts usually decide probate issues involving wills and trusts. Federal courts hear bankruptcy issues.
The so-called “probate exception” normally keeps federal courts from hearing such disputes, but there is no congressional law mandating the hands-off approach.
“The probate exception does not bar federal courts from adjudicating matters outside those confines and otherwise within federal jurisdiction,” wrote Justice Ruth Bader Ginsburg for the court.