I've got two problems with that.
Firstly, I find hanging the kind of rung we're talking about a lot easier when locked, at any angle from the neck down. To me it seems common sense to train it the hardest way I can, then when I get into an easier position it'll be even easier, something like that anyway.
Secondly, locking is mostly about the biceps and lats, which are much stronger muscles than the finger flexors when hanging on to a crappy rung. By locking on a crap rung, your fingers are going to fail a long time before your biceps and lats will, meaning they're not getting a proper work out. The finger flexors are much more efficient when holding a bar, so I train locks on a bar instead where I can add much more weight to myself.
