If you run your code through perl -MO=Xref mytest.pl, you'll get the following output...

----- unneeded portion of output not shown -----
    Package aaa
      &do_a             s14
    Package bbb
      &do_b             s24
    Package ccc
      &do_c             s25
  Subroutine (main)
    Package (lexical)
      $var              i10, i21, i34, 27
    Package aaa
      &do_a             &23
    Package bbb
      &do_b             &24
    Package ccc
      &do_c             &25
  Subroutine aaa::do_a
    Package (lexical)
      $var              13
  Subroutine bbb::do_b
    Package (lexical)
      $var              37
  Subroutine ccc::do_c
    Package (lexical)
      $var              48
mytest.pl syntax OK
[download]

The important part of all that is:

    Package (lexical)
      $var              i10, i21, i34, 27
[download]

That's saying that $var is being declared in line 10, 21, and 34. ...and used in 27. This confirms what others have previously mentioned in this thread; that packages don't create their own lexical scopes. Files create lexical scope, and curly brackets do. So it's common to think of a package as its own lexical scope, since it's also common (though not a requirement) for packages to live alone in a file. But you can't rely on that logic because multiple packages in the same file reside in the same scope.

Update: On a side note, I do think that B::Xref's output is a little misleading by saying, "Package (lexical) $var .....". It seems that it ought to say something more akin to "File (lexical) $var" or "Block (lexical) $var ..."

I'm kind of interested in hearing the reason for why it does what it does.