Isn't understanding the capabilities of the people they manage the job of the manager? I always thought that was the whole point. If they don't know this, then maybe they shouldn't be making any promises at all.
Making correct estimate on how much time feature will take is something different then just understanding the capabilities of the people.
Even developers themselves are often unable to produce good estimates. In fact, most developers tend to systematically underestimate how much time they will need for this or that task.
I have seen management to even add padding to estimate and it is still not enough in the end.