That duplication trick is really not nice, but I don't see a way how can this be avoided in perl5 (probably a wiser monk may shed some light on this).
Some other languages have nicer constructs for recursive anonymous functions without this trickery, look at a few examples at stackoverflow.com.
However I treated the challange of "eliminating named variables", more as a (math-like) challange of using functional programming concepts in perl5, rather than "how to achieve tha same results in real code".
we have just traded the name of a hash for a name of a sub [...], so it's not a real gain
That's true for the particular code above, however think of this issue more generally. If we insist on retaining the sub identifier, that still has its advantages, because in lots of code, we traded lots of hash identifiers for one sub identifier.