Actually it's exactly that: within the Sol system we know DNA was favored. The lack of evidence of other encoding systems strongly suggests that at the very least, once DNA happens it outcompetes everything else in Earth-like biospheres. Since we're looking for life in Earth-like locales - and Enceladus is targeted for that reason - then it's reasonable to expect we'd find DNA.
The benefit of DNA is it's conclusive: if we find DNA, then life (or an exceptionally bizarre natural process) must be their, and if we grab a sequence then it's high probability we'll be able to figure out what type of life it is due to some Earth-local proteins being basically limited in improvement by physics itself, and heavily conserved - i.e. even totally alien life would be expected to manufacture a close analogue.
Not to mention that if we turn up something totally weird, we can still synthesize it up in a lab to study.
The benefit of DNA is it's conclusive: if we find DNA, then life (or an exceptionally bizarre natural process) must be their, and if we grab a sequence then it's high probability we'll be able to figure out what type of life it is due to some Earth-local proteins being basically limited in improvement by physics itself, and heavily conserved - i.e. even totally alien life would be expected to manufacture a close analogue.
Not to mention that if we turn up something totally weird, we can still synthesize it up in a lab to study.