Chris Thile and siblings Sean and Sara Watkins, collectively known as Nickel Creek, have been widely embraced by the bluegrass and acoustic-music communities, even though their music makes a habit of stretching or ignoring genre boundaries. How have they gotten away with such apostasy? "Talent" is probably too facile an answer, but it's the best one available. On Why Should the Fire Die?, their latest release on Sugar Hill Records, the Creekers work with producers Eric Valentine and Tony Berg, whose rock credentials result in a bigger-than-usual sound on tracks such as the darkly evocative "When in Rome," "Best of Luck," with a lead vocal by Sara that's tougher than anything she's recorded to date, and "Helena," which (gasp!) actually uses drums. Under typical circumstances, purists would be up in arms over this type of eclecticism, but the quality of the tunes helps blunt the argument that Nickel Creek should limit itself in any way. Thile and the Watkinses, presently traveling with Andrew Bird, get away with breaking plenty of musical rules. May they continue to be rewarded for their misbehavior.