[Haskell-cafe] Why does HXT use Arrows?

Something I have been wondering for a while is: Why is HXT built on arrows, rather than monads? I understand that arrows are a generalization of monads, but they also add extra complexity that is often unnecessary. Furthermore, as I understand it they only give you additional power when your arrow cannot implement ArrowApply, since otherwise your arrow is equivalent to a monad anyway, and it looks like the result of parsing an XML document gets you an arrow which implements ArrowApply. Is there some circumstance I am missing where the fact that HXT uses arrows rather than monads lets one do something that one couldn't have done with monads? Cheers, Greg