"Nein, er wird den Fisch um nichts mehr bitten."
Again, I don't want to claim a universal rule here, but the general usage patterns go in the direction you suggest. Some verbs require the dative, others the accusative and some can take either or both (e.g. 'informieren' and 'benachrichtigen' require the accusative). There is no foolproof rule from which you could infer to which group a given verb belongs. But the tendency is clearly as observed by you above. If a 'speaking verb' takes both objects, the dative object is the person you address and the accusative object is the thing you want to say. It's similar for other verbs that take both kinds of objects. So, my answer is: yes, but take it ('it' being 'asking verbs take the accusative') as a rule of thumb, not a heavenly truth. Maybe you find this useful: http://german.about.com/library/verbs/blverb_dativ.htm