Phosphorous is used by all previously known life in a number of ways, including as part of the DNA backbone. If there's something that uses something else, it's a big deal.
It's a proof-of-concept for radical new ideas of where/how life can form.
For instance, Titan has a thick atmosphere and lakes of liquid ethane/methane. If Arsenic-based life exists, could there be Methane-based life in those depths?
Right, I guess 'methane-based life' was poor wording. Suffice it to say that this discovery implies that life can form in ways and places that we've never considered.
