alt Hacker NewsIndeed. Regexes are _regular_, which is non hierarchical by definition.
The two are useful for different layers of abstraction: regex is for lexing and PEG is for parsing.
Speaking of the Chomsky hierarchy, last I checked, it is still unproven whether or not PEGs can parse all context free languages. Intuitively, they're _probably_ weaker than CFGs, but no one has yet provided a counter example.
PEGs aren't contained within the context-free languages, so it's not really intuitive that they're weaker, particularly as nobody has yet come up with a context-free language that a PEG cannot parse. They're capable of parsing things context-free grammars cannot.