The question is in the title: from what I read in the answer to another question, Artin L-functions are conjecturally cuspidal automorphic L-functions for some algebraic group that can be transfered to $GL\_{n}$. On the other hand, elements of the Selberg class are widely believed to be (cuspidal?) automorphic L-functions for $GL\_{n}$. So where exactly lies the difference between those two sets of L-functions?  

Thanks in advance.