Agreed its a clumsy demonstration. However, I have seen the memory returned in more realistic situations. For example, if you copy a large array when sorting it

my @a = 1 .. 100000;
@a = sort{ $b <=> $a } @a;
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When I run this code, I can watch the memory usage peak at around 21 MB, but then fallback to around 18 MB. So even in this fairly simple and common operation, some memory is being returned to the OS. Not all of it, as loading the array only consumes around 8 MB, so the post sort figure of 18 shows that a considerable amount of "working storage" hasn't been returned to the OS. If you then empty the array @a = ();, another 3 or 4 MB is released. Interestingly, if you then undef @a; another 1 MB or so is released. Skipping the null list assignment step takes you straight to the (same) final position.

It would be a labour of love to try and understand what and when this occurs enough to be able to reliably make use of the information, so the your basic point about essentially ignoring it probably sage advice in most situations.