Calling 4th a 'miniature combat game' helps me, in my brain, to distill the differences in approach these games have. Its just one way of looking at it.
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The reason, I think, that these thread go round and round and never end has to do with the basic fundamentals of what makes these games different beasts, but trying to get to the heart of that difference usually leads to a lot of misunderstandings and defensiveness.
The approach I try to use is to start from the fact that the person I'm talking to is playing an RPG, and then try to reason back from that - "Given this person is (i) playing and RPG, and (ii) wants this thing that strikes me as really weird, what are they doing differently from me, or what do they value differently from me, such that in their framework it makes sense."
I find it also helps to know what sorts of other RPGs they might have experience with, because this can help hone in on other models of play.
DMZ has suggested that because of so much structure in 4th why do you even need a DM? Why not just use a computer.
But 4e, at least as most people play it, clearly does involve a GM. So what is the GM for? What does [MENTION=27160]Balesir[/MENTION] have in mind?
Luckily, he told us himself upthread! I haven't got the quote ready-to-hand, but my paraphrase is along these lines: I want the GM to be able to frame challenging situations for the players, and then, in the resoution of those situations, I want the GM to go no holds barred for the NPCs and monsters, and the players to go no holds barred for the PCs, and by application of the mechanics we'll find out who overcomes whom, or what compromise is reached.
If the GM has to not only play the NPCs but also "be" the mechanics, than this approach breaks down - because the GM now has a conflict of interest between playing the NPCs as hard as s/he can, and being a fair resolver of conflicts between them and the PCs.
But that doesn't mean you can replace the GM with a computer. The computer can't play NPCs with personality. The computer can't decide that, because of how you spoke to his manservant, you have a -2 penalty on your Diplomacy rolls with the king. Generally, the computer can't provide colour in the same way a GM can (better visuals, worse patter) and can't adjudicate fictional positioning in anything like the same way.