I don't think they're simplistic, they just serve a different purpose. UW2 illustrates this point really well by using both trees and the U4-like keywords. The dialog trees are for holding actual conversation, meeting people, and so on, but then you can use keywords with many NPC's to ask for specific information. The keyword usage was particularly interesting when the word you needed to use made no sense in context of the conversation or what the NPC was revealing to you, but you knew to use it because of information you had previously acquired elsewhere. Take Altara; she's a sleeper agent and will obviously not hint in any way at her true allegiances, so there's no dialog option to call her out or anything, but if you freed Bishop then you know to ask, and can do so through typing the keyword. I really like this approach.