I'm wondering too if it depends on the kid? Nat is very unconcerned, so it seems like the incentive or whatever isn't quite there yet? We have a pretty good system for when it happens (she refuses to wear pull ups) - I have a couple of brolly sheets & she redresses herself, we're usually done in a few minutes & back to sleep. If it ramps up over winter (and I'm expecting it will) we will start to tackle it soonish I think.
It's probably very individual as to when. I guess, like so many other things, once the system isn't working anymore it's time to find a new one.