The Gizmodo article only says that these new bacteria have arsenic instead of phosphorus in their DNA, which is not enough information to understand just how ground-breaking it is. Mind you, arsenic is in the same group as phosphorus, so their chemical properties are comparable. If the rest of their chemical makeup is the same (deoxyribose for a sugar, same set of nitrogenous bases, etc), then it's most probable that they evolved from regular bacteria under the extreme conditions of that lake (such as lack of phoshorus and over-abundance of arsenic). While that would be extremely interesting for biochemists, microbiologists and other scientists, it won't change our general understanding of life much.
Now, if arsenic was just the first indication that this form of life is different, and further study will reveal completely different biochemistry as well, then we can talk about possible implications for extra-terrestrial life and all that universally exciting stuff.