I'd agree that consistency can be a good reason, but AFAIK, both
styles of oo are used in Launchpad, so either would be inconsistent.
And I also think that any JavaScript programmer ought to be familiar
with JavaScript's native oo. They'll encounter it sooner or later,
perhaps even when debugging their own YUI-oo objects.
As a concrete example of the consistency issue, we had/have
several different mockio implementations and it was/is a nightmare
trying to figure out which one to use.
I am sorry I gave you nightmares, but at the time I implemented
IORecorder (now unified with the lazr-js one as MockIo by henninge), I
could not find another implementation. I believe I implemented
IORecorder essentially in parallel with lazr-js being integrated into
the tree.