Well...for currencies besides Dash the risk is somewhat reduced by the fact that the effects of such a backdoor can immediately be observed, whereas with Dash the "spork" model means that an exploit can be hidden away and only activated at a later stage, or the network can be remotely forked by anyone who holds the spork key.
BTW: the effects of the backdoor can be observed in both cases when it is used, and not any earlier. So there is really no difference in that regard. The forking is of course possible, but that is easily observable, too, or am I missing something?